Effects of dietary protein level and age at photo stimulation on reproduction traits of broiler breeders and progeny performance

Effects of dietary protein level and age at photo stimulation on reproduction traits of broiler... ABSTRACT A study with a 2 × 2 factorial arrangement was conducted to determine the effects of 2 dietary crude protein levels, high (CPh) or low (CPl), supplemented with free amino acids (AA), and 2 ages at photo stimulation (PS)—early (21 wk; PSe) or late (23 wk; PSl)—on reproduction traits of broiler breeders and progeny performance. Diets were isocaloric, and calculated CP content of the CPl diets was 15 g/kg lower than the CPh diets during all phases. A total of 480 female and 64 male Ross 308 breeders of 20 wk of age were used. Total egg production was similar between CPl and CPh birds during phase 1 and 2 but was reduced by 2.8 eggs for CPl birds during phase 3. For the overall laying period, CPl birds tended (P = 0.075) to produce 4.7 fewer total eggs. Hatchability of set eggs was similar between CPl and CPh birds during phases 1 and 2 but tended (P = 0.064) to be lower for CPl birds in phase 3. PSe birds showed an advanced age at sexual maturity and age at peak production of 4.6 and 5.3 d, respectively, resulting in 2.5 more total eggs during phase 1. During phase 1, PSe birds showed an almost 5% increased fertility. Chick production in phase 1 was higher for PSe birds resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks. Progeny from early PS breeders showed an overall significant lower feed conversion ratio (FCR). It was concluded that egg and chick production during phases 1 and 2 were not affected by dietary CP level, but egg and chick production was reduced for CPl birds during phase 3. On the other hand, PSe birds showed an increased number of chicks. It is possible to decrease CP level of breeder diets with comparable reproduction from 22 to 46 wk; however, this is questionable for phase 3. For maximal chick production, early PS is recommended. INTRODUCTION The last 5 to 6 decades have shown an increased genetic potential of broiler breeders for body weight gain due to selection of the progeny (Havenstein et al., 2003a, 2003b; Renema et al., 2007; Zuidhof et al., 2014). Although the poultry breeding companies have worked to maintain or even increase the rates of egg production and hatchability (Laughlin, 2009), achieving these potentials at the broiler breeder farm level on a consistent level has proven to be more challenging (Renema et al., 2013). Therefore, optimization of the diet (protein to energy ratio) and management is necessary to achieve maximal reproduction (Van Emous, 2015). It has been reported that feeding high levels of crude protein (CP), especially lysine, to broiler breeders will lead to over-fleshing (De Beer, 2009). This extra breast muscle requires energy input to prevent potential negative effects on lay persistency. Furthermore, Lopez and Leeson (1995a) clearly illustrated the negative effect of excess CP on fertility, and Ekmay et al. (2013) identified lysine and isoleucine as 2 amino acids (AA) directly affecting fertility in breeders. Pearson and Herron (1982) reported that low protein intake (21 vs. 27 g/d) improved hatchability due to a decreased embryonic mortality. An additional benefit of feeding breeders a low-CP diet is the decreased nitrogen excretion due to the lower nitrogen intake and higher nitrogen retention (Lopez and Leeson, 1995b). Feeding the breeders not only affects the breeders themselves but also the progeny (Zuidhof et al., 2014). However, relatively few papers are available on the effects of specific protein or AA intake of broiler breeders on offspring performance and slaughter yields (Lopez and Leeson, 1995c; Mejia et al., 2013; Van Emous et al., 2015a; Van Emous, 2015). Age at photo stimulation (PS) varies globally and may affect production performance of broiler breeders. In some regions, breeders are stimulated around 21 wk of age while in others, this is around 23 wk of age mainly due to the differences in threshold for minimal hatching egg size (minimum egg weights of 50 and 52 g, respectively). Most breeder farms currently delay age at PS until the flock is 21 to 23 wk of age (Joseph et al., 2002). Joseph et al. (2002) also stated that later PS breeders generally compensate for a later age at sexual maturity with an increased rate of lay. This was underlined by several authors who found no effect of age at PS on egg production during the overall laying period (Yuan et al., 1994; Robinson et al., 1996; Renema et al., 2001a; Joseph et al., 2002). No effects of age at PS on incubation traits were found in the studies of Robinson et al. (1996) and Renema et al. (2001a). In the study of Robinson et al. (1996), however, they found a higher chick production when birds were PS at 140, 150, or 160 d compared to 120 and 130 d. No literature is available on the effect of age at PS on progeny performance. As shown above, dietary CP level and age at PS can affect production performance of breeders. Most research, however, was carried out ∼15 years ago and modern broiler breeder strains differ genetically since that time (Havenstein et al., 2003a, 2003b; Renema et al., 2007; Zuidhof et al., 2014). Moreover, little is known about the combined effects of dietary CP level during lay and age at PS. Therefore, the objective of this study was to determine the effects of dietary CP levels during lay and age at PS on reproduction of Ross 308 broiler breeders and progeny performance. MATERIALS AND METHODS The protocol for the experiment conformed to the standards for animal experiments and was approved by the Ethical Committee of Wageningen UR, the Netherlands. Experimental Design The study was conducted as a 2 × 2 factorial completely randomized block design with 2 maternal dietary CP levels and 2 ages at PS. The birds received 2 diets with different levels of CP: high CP (CPh) at breeder recommendations, and low CP (CPl) (Table 1). Diets were formulated to be isocaloric (2,800 kcal/kg nitrogen corrected apparent metabolizable energy [AMEn]) and the calculated CP content of the CPl diets was 15 g/kg lower than the CPh diets during all phases (phase 1: respectively). Each phase had the following duration: phase 1: 22 or 24 to 34 wk of age (for early and late PS, respectively), phase 2: 35 to 46 wk of age, and phase 3: 47 to 60 wk of age. Experimental diets were formulated according to the recommendation of the breeder company and supplemented with free AA (Lys, Met, Thr, Trp, Arg, Ile, Val) (Aviagen-EPI, 2015). Breeders were reared (20 lx) at a photoperiod of 8L:16D (07:30 to 15:30) and photo-stimulated with 11 h of light (40 lx) at early (21 wk = PSe) or late age (23 wk = PSl). After PS, day length was gradually increased (22 or 24 wk of age = 12L:12D; 23 or 25 wk of age = 13L:11D; 24 or 26 wk of age = 13.5L:10.5D for PSe and PSl, respectively) to a photoperiod of 14L:10D at 25 (PSe) or 27 (PSl) wk of age. This was maintained until the end of the experiment at 60 wk of age, with light on from 0330 to 1730 h (40 lx). During the experiment, birds fed the different diets received the same daily amount of feed according to the growth pattern of the CPh diet. This resulted in a different daily nutrient intake (particularly CP and AA) for the CPl diet birds (Table 2). Table 1. Dietary ingredients, and analyzed and calculated nutrients of the breeder diets (g/kg, as-fed basis).   Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00    Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00  1Dietary protein level. CPh, high dietary protein level lay; CPl, low dietary protein level lay. 2Provided per kilogram of complete diet: vitamin A, 10,000 IU; vitamin D3, 1,500 IU; vitamin E, 100 mg; vitamin K3, 3.0 mg; vitamin B1, 3.0 mg; vitamin B2, 10.0 mg; vitamin B6, 4.0 mg; vitamin B12, 0.03 mg; niacinamide, 30 mg; D-pantothenic acid, 16.3 mg; choline chloride, 344 mg; folic acid, 2.0 mg; biotin, 0.3 mg; iron, 100 mg; copper, 15 mg; manganese, 100 mg; zinc, 100 mg; iodine, 2.0 mg; selenium, 0.15 mg. 3CVB matrix values (CVB, 2011) were used for diet formulation. View Large Table 1. Dietary ingredients, and analyzed and calculated nutrients of the breeder diets (g/kg, as-fed basis).   Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00    Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00  1Dietary protein level. CPh, high dietary protein level lay; CPl, low dietary protein level lay. 2Provided per kilogram of complete diet: vitamin A, 10,000 IU; vitamin D3, 1,500 IU; vitamin E, 100 mg; vitamin K3, 3.0 mg; vitamin B1, 3.0 mg; vitamin B2, 10.0 mg; vitamin B6, 4.0 mg; vitamin B12, 0.03 mg; niacinamide, 30 mg; D-pantothenic acid, 16.3 mg; choline chloride, 344 mg; folic acid, 2.0 mg; biotin, 0.3 mg; iron, 100 mg; copper, 15 mg; manganese, 100 mg; zinc, 100 mg; iodine, 2.0 mg; selenium, 0.15 mg. 3CVB matrix values (CVB, 2011) were used for diet formulation. View Large Table 2. Daily crude protein (CP) and amino acid intake of broiler breeders from 21 to 60 wk of age.1 Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  1Values based on analyzed content of the diets. AA levels in the CPl diets were supplemented with free AA to the recommend level of the breeder company. 2FI, Feed intake. 3CPh, high dietary protein level lay; CPl, low dietary protein level lay. 4Values between parentheses are for the late PS birds. 5Weighted average of all weeks. View Large Table 2. Daily crude protein (CP) and amino acid intake of broiler breeders from 21 to 60 wk of age.1 Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  1Values based on analyzed content of the diets. AA levels in the CPl diets were supplemented with free AA to the recommend level of the breeder company. 2FI, Feed intake. 3CPh, high dietary protein level lay; CPl, low dietary protein level lay. 4Values between parentheses are for the late PS birds. 5Weighted average of all weeks. View Large Housing and Management Breeders A total of 480 female and 64 male Ross 308 broiler breeders of 20 wk of age (PoultryPlus, Ambt Delden, The Netherlands) were used in this experiment. Breeders were fed during the pullet phase a commercial 4-phase feeding program (starter-1 diet: d 0 to 14, starter-2 diet: d 15 to 42; grower diet: d 43 to 105, pre-breeder diet: d 106 to 140). The starter-1, starter-2, grower, and pre-breeder diets contained 2,800, 2,800, 2,600, and 2,700 AMEn kcal/kg; 20.0, 17.0, 13.5, and 14.5% CP, respectively. The breeders were housed in 16 floor pens (1.8 × 4.0 m = 7.2 m2) with 34 birds (30 females and 4 males) per pen at the start of the laying period (20 wk of age) in 2 separated mechanically ventilated experimental broiler breeder rooms (8 pens per room). Between 20 and 27 wk of age, the 2 main rooms were divided in 2 different temporary light-tight compartments by wooden partitions. All 4 compartments were divided in 4 different pens, which resulted in total 16 pens. Each pen contained a laying nest, 2 feeding troughs for females (6 m length), a separate feeding pan for males, and 7 drink cups above the slatted plastic floor (1.8 × 1.0 m). The remaining area was bedded with wood shavings (2.0 kg/m2). Males received a commercial male diet (2,600 kcal/kg AMEn; 13.0% CP; 0.45% dig. Lys; 0.5% dig. M+C; 1.0% Ca; 0.3% aP). During the first 2 (PSe) or 4 (PSl) weeks birds received a standard pre-breeder diet according to the recommendation of the breeder company (Table 1). During the experiment, birds were maintained on the same target body weight (BW) and feed allocation was adjusted to the predetermined body growth curve during rearing and a combination of the predetermined body growth curve and egg production (Aviagen-EPI, 2015). Water was provided ad libitum and temperature was maintained at 20°C. Housing and Management Progeny A total of 384 1-day-old Ross 308 broiler chicks (192 female and 192 male) were used from hatching eggs of 50 wk of age for a growth trial from 0 to 35 d of age. After feather sexing, male and female chicks were randomly allotted to 32 floor pens (1.1 × 0.9 m), with 12 chicks (female or male) per pen. The broiler unit was illuminated continuously during the first 2 d and from d 3 onwards according to the schedule 18L:6D. A commercial 3-phase broiler feeding program (starter diet: d 0 to 11, grower diet: d 12 to 27, finisher diet: d 28 to 35) was provided to all chickens and feed and water were supplied ad libitum during the entire experimental period. The starter, grower and finisher diets contained 3,060, 3,180, and 3,225 AMEn kcal/kg; 22.3, 20,1, and 18.7% CP; 1.19, 1,06, and 0,96% dig. Lys; 0.88, 0,81, and 0,75% dig. M+C, respectively. Diets were formulated to meet or exceed the nutrient recommendations of the breeder company. Observations Body Weight To monitor BW and BW gain, 10 females (as group) and 1 male per pen were weighed weekly from 20 to 60 wk of age in the morning before feeding. At 20 and 60 wk of age, all birds per pen were weighed. Egg Weight, ASM and Peak Egg Production Egg weight of all hatching eggs (settable and small) of d 1 (Monday) were measured and recorded on a weekly basis. Average egg weight per phase was calculated. Age at sexual maturity (ASM) was defined as age at 50% production and was determined by a linear interpolation of the week (in days) where birds passed 50% rate of lay. Peak egg production was determined as a 3-wk rolling average. Egg Production All eggs per pen were collected, graded, and recorded daily. The total number of settable (above 50 g), small (under 50 g), double yolk, abnormal shell, dirty, and floor eggs were calculated per pen, per week and per feeding phase. Mortality Mortality was recorded daily per pen to calculate total percentage of mortality per week, feeding phase, and total laying period. Mortality was categorized as leg problems and other causes. Incubation Traits and Chick Production Incubation traits were measured at 28, 34, 40, 46, 50, and 56 wk of age. Per age, 150 eggs per pen from 6 to 9 d production period were transported and set, after an approximately 5- to 7-d storage period (16 to 18°C and 50 to 60% relative humidity), in an incubator at a commercial hatchery (Lagerwey, Lunteren, The Netherlands). At d 18, eggs were transferred to hatcher baskets and placed in an incubator. At d 21 of incubation, unhatched eggs were opened to determine stage of embryonic mortality. The following stages of embryonic mortality were used to classify the dead embryos: d 1 to 11 (early stage to feather follicle visible), d 12 to 17 (small embryo with feathers), d 18 to 21 (full grown dead embryo or live in shell). All chicks were graded as first- or second-grade chicks, wherein a first-grade chick was defined as dry, free of deformities, and bright eyes (Tona et al., 2004). BW of first-grade chicks were recorded. Fertility was calculated as the percentage of fertile eggs of the set eggs. Hatchability of set and fertile eggs was calculated as the percentage of all chicks hatched of set and fertile eggs, respectively. Embryonic mortality was calculated as a percentage of fertile eggs. Second-grade chicks were calculated as a percentage of total hatched chicks. Chick production was calculated using the mean hatchability of set eggs for each pen and multiplied by its settable egg number per phase and overall laying period. Progeny performance BW of the broilers in each pen was determined at d 0, 11, 27, and 35. Feed intake, BW gain, and feed conversion ratio (FCR) in each pen were recorded and calculated for the periods d 0 to 11, 12 to 27, 28 to 35, and 0 to 35. Mortality was recorded daily. Live weight, weight of carcass, wings, legs, back and breast meat were recorded at d 35 by slaughtering 4 birds (at random) per pen. Carcass yield was calculated as percentage of live weight of the broiler whereas wings, legs, back and breast meat were calculated as percentage of carcass weight. Statistical Analysis Raw data were analyzed for statistical outliers. Significant outliers (values deviating more than 2.5 times the standard deviation from the mean value) were not included in the data subjected to statistical analysis. The experimental data were analyzed using Genstat statistical software (Genstat, 2015). Statistical significance was declared at P ≤ 0.05, with 0.05 < P ≤ 0.10 considered as a tendency. Response parameters were analyzed using analysis of variance (ANOVA) according the following model: Yijk = μ + Blocki + CP dietj + Age at PSk + (CP diet * Age at PS)jk + εijk where Yijk was the dependent variable, μ was the overall mean, Blocki (4 compartments) was the random block effect (i = 1…4), CP dietj was the effect of CP diet (j = 1…2), Age at PSk was the effect of age at PS (k = 1…2), CP diet * Age at PSjk was the interaction effect between CP diet and age at PS and εijk was the residual error term. Pen was the experimental unit. The statistical model for progeny performance included sex (male and female). RESULTS AND DISCUSSION Body Weight A 9% lower total CP intake for the birds fed the CPl diet did not (except at 34 wk of age) affect BW of the birds during the laying period (Table 3). This was in line with data of previous studies of Pearson and Herron (1981); Lopez and Leeson (1995a); Joseph et al. (2000), and Mohiti-Asli et al. (2012). As suggested by several authors, BW of breeders seems to be more affected by energy than by protein intake per se (Pearson and Herron, 1981; Spratt and Leeson, 1987; Keshavarz and Nakajima, 1995; Mohiti-Asli et al., 2012). Table 3. Body weight (g) at 20, 24, 34, 46 and 60 wk of age as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. View Large Table 3. Body weight (g) at 20, 24, 34, 46 and 60 wk of age as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. View Large Concurring with previous research of Robinson et al. (2007), no effects of different PS on BW were observed at onset of lay (20 and 24 wk of age) (Table 3). Egg Weight, ASM, and Peak Egg Production Daily CP intake did not affect overall egg weight (Table 4), consistent with the studies of Pearson and Herron (1981); Joseph et al. (2002); Mohiti-Asli et al. (2012), and Van Emous et al. (2015b; between 22 and 45 wk of age). In the study from Van Emous et al. (2015b) daily CP intake of 20.5, 22.0 or 23.5 g/d did not affect egg weight during the first phase of lay; however, during the second phase of lay breeders fed 19.4 g/d CP daily showed a lower egg weight than breeders fed 21.5 g/d. In the previous mentioned studies of Pearson and Herron (1981); Joseph et al. (2000); Mohiti-Asli et al. (2012), and Van Emous et al. (2015b), breeders on the lowest daily CP intake received 21.3, 20.8, 25.7 and 20.5 g/d, respectively. Table 4. Egg weight, ASM, peak egg production, and age at peak egg production as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42    Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Egg weight was determined for all hatching eggs (small and settable). 3ASM, age at sexual maturity, defined as age at 50% production. 4Determined as a 3-wk rolling average of %hen d. View Large Table 4. Egg weight, ASM, peak egg production, and age at peak egg production as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42    Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Egg weight was determined for all hatching eggs (small and settable). 3ASM, age at sexual maturity, defined as age at 50% production. 4Determined as a 3-wk rolling average of %hen d. View Large Egg weight during the overall laying period was not affected by age at PS (Table 4), which was consistent with previous studies (Yuan et al., 1994; Robinson et al., 1996; Renema et al., 2001a; Pishnamazi et al., 2014). Contrary to our results, Joseph et al. (2000, 2002) found that birds that were photo stimulated at 23 versus 21 wk of age produced heavier eggs throughout the overall laying period. They postulated that this was mainly caused by a higher BW during the first part or overall laying period. In the current study no effect on BW during the initial and overall laying period was observed which explained the absence of differences in egg weight. Age at sexual maturity was not affected by differences in daily CP intake (Table 4) which concurred with studies of Pearson and Herron (1981); Spratt and Leeson (1987); Lopez and Leeson (1995a), and Joseph et al. (2000). Contrary to those findings, Van Emous et al. (2015b) observed a delayed ASM of 1.4 d when breeders received a 10% higher daily CP intake during initial lay. In the latter study, however, an opposite advanced peak egg production of 8.5 d was found. They postulate that this was caused by the higher daily CP intake which stimulates the development of the reproductive tract (Lilburn and Myers-Miller, 1990). The reason for the absence of an effect on ASM in the current study, may be due to the fact that the difference in daily CP intake (21.3 vs. 19.3 g/d) between the treatments was not distinctive enough. Late PS birds showed a delayed ASM (P < 0.001) and age at egg peak production (P = 0.029) of 4.6 and 5.3 d, respectively (Table 4). Age at sexual maturity, in the current study, was delayed by 0.33 d per d that PS was delayed. This was in close agreement with Renema et al. (2001b), and Pishnamazi et al. (2014) who found an increase of 0.35 and 0.40 d, respectively, per d that PS was delayed. A maturation rate of 0.36 d per d that PS was delayed was calculated by Lewis (2006). Robinson et al. (1996); Joseph et al. (2002), and Ciacciariello and Gous (2005) found lower maturation rates of 0.22, 0.27, and 0.21 d, respectively, per day that PS was delayed. Neither peak egg production and age at peak egg production were influenced in the current study by daily CP intake (Table 4). This is consistent with Spratt and Leeson (1987), but in contrast with Lopez and Leeson (1995a). The latter authors reported that birds fed a 16% CP diet reached the highest and the most persistent peak production. However, due to a difference in persistency in the second part of lay, no effect on total egg production at the end of lay was observed in that study. No effect of age at PS on peak egg production was found in the current study (Table 4). In the literature, only 1 study (Yuan et al., 1994) is available that shows some information about peak egg production. Yuan et al. (1994) found that breeders PS at 14 and 17 wk of age showed a higher number of early egg production (until 30 wk of age) and a lower peak egg production compared to breeders PS at 20 wk of age. The difference between the current and the study of Yuan et al. (1994) is that the latter authors applied extreme early ages at PS (14 and 17 wk of age), which is not relevant under practical circumstances. Egg Production Reductions of 15 g/kg of dietary CP levels during phase 1 (22 or 24 to 34 wk of age) and phase 2 (35 to 46 wk of age) did not affect total egg production and settable eggs compared to the CPh diet (Table 5). In phase 3 (47 to 60 wk of age), reductions of CP levels from 13.0 to 11.5% reduced (P = 0.043) total egg production. This resulted in a tendency (P = 0.075) to a lower total egg production (183.5 vs. 188.2 eggs/hen housed) for the overall laying period (22 or 24 to 60 wk of age) for birds fed the CPl diet (19.3 g CP/bird/d). In contrast with the current study, Pearson and Herron (1981); Spratt and Leeson (1987), and Lopez and Leeson (1995a) found no effects on egg production when birds were fed a low daily CP intake (21.3, 16.9 and 14.9 g CP/bird, respectively). An opposite effect was reported by Whitehead et al. (1985); who found a higher egg production when breeders were fed a lower daily protein intake (20.5 vs. 25.2 g CP/bird). Joseph et al. (2000) found a lower numerical egg production for birds fed 14 compared to 16 and 18% CP diets; however, they carried out the experiment between 24 and 29 wk of age. The difference in effect on egg production due to the different daily protein intake in phase 3 in the current study might be explained by a low dietary electrolyte balance (DEB) level of the CPl diet. To achieve an 11.5% CP diet, a very low level of soybean meal was used, which resulted in a K content of 5.3 g/kg and a DEB of 150 mEq/kg. Dos Santos et al. (2011) reported that broiler breeders from 55 to 66 wk of age had decreased egg production when fed diets with a DEB of 150 mEq/kg compared to 180 mEq/kg. Recent research of Halley et al. (2016), using Ross 708 broiler breeders, reported that levels of 180 and 205 mEq/kg analyzed DEB significantly improved egg production in wk 50 compared to breeders fed a diet with 160 mEq/kg. The severe reduction in DEB during phase 3 for the CPl diet in the current study may have been involved with the reduction in egg production during this phase. Table 5. Egg production traits and defective egg production (n/hen) during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Settable eggs, normal egg ≥ 50 g. 3Small eggs, normal egg < 50 g. 4Abnormal shell eggs, cracked, soft shell and shell less eggs. 5Floor eggs, eggs laid outside nests (in litter or on slats). View Large Table 5. Egg production traits and defective egg production (n/hen) during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Settable eggs, normal egg ≥ 50 g. 3Small eggs, normal egg < 50 g. 4Abnormal shell eggs, cracked, soft shell and shell less eggs. 5Floor eggs, eggs laid outside nests (in litter or on slats). View Large A higher number (2.3 vs. 1.5%) of abnormal-shell eggs (cracked, soft shell, and shell-less) during the overall laying period were found for birds fed the CPl diet (P = 0.028), which was mainly caused by the higher number of abnormal-shell eggs in phase 3 of lay (Table 5). Possible dietary factors that affect eggshell quality are calcium intake, available phosphorus intake, and ingredients. In the current study, all these factors were equal, and therefore it is hypothesized that the low level of DEB may have been related with the increased number of abnormal-shell eggs in the CPl group. In the current study, early PS birds produced in the first phase 2.5 more total, 2.6 more settable, 0.9 more small, and 1.2 fewer floor eggs (Table 5). Egg production during the overall laying period, however, was not affected by age at PS. This result for the overall laying period was previously found by Yuan et al. (1994); Robinson et al. (1996); Renema et al. (2001a), and Joseph et al. (2002). The latter authors stated that later PS breeders generally compensate for a later age at sexual maturity with an increased rate of lay. Not surprisingly, the early PS birds in the current study produced more small eggs (2.7 vs. 1.8) during phase 1. In a previous study of Renema et al. (2001a) initial egg weight was decreased (43.9 vs. 46.0 g) for early PS breeders (19 vs. 21 wk of age). This difference in egg weight was caused by the 4.9 d earlier age at sexual maturity, lower BW at onset of lay (2,547 vs. 2,681 g) of the breeders, and an 11.5% lower liver weight of early PS birds, which limits the production of yolk precursors and thus also egg weight (Renema et al., 2001b). Mortality No effect of different daily CP intake was found on mortality (data not shown), which is contrary to Lopez and Leeson (1995a) who found a trend to a lower mortality when birds were fed a 10% CP diet. An opposite effect was shown by Van Emous et al. (2015b) who found an increased mortality during the first phase of lay (22 to 45 wk of age) for birds fed the lowest daily CP intake. The majority of the mortality was due to an increased incidence of ruptures of the gastrocnemius tendons. They hypothesized that this was caused by competitive feeding behavior resulting in (hyper)activity like running and jumping, inducing a higher risk of damaging the tendons. This competitive feeding behavior was avoided by additional feeding space in the current study. Incubation Traits and Chick Production In the current study, fertility was not affected by differences in daily CP intake (Table 6), which was also reported by Whitehead et al. (1985); Mejia et al. (2012), and Van Emous et al. (2015b). Other studies, however, showed that feeding broiler breeders a high daily protein level during the laying period resulted in decreased fertility (Lopez and Leeson, 1995a; Ekmay et al., 2013). It is not clear what caused the differences between the current and latter cited studies, but possible causative factors are: housing system, breed, amount of feed, energy to protein ratio, and energy level. Moreover, body composition of broiler breeders has changed dramatically during the last decades to a much leaner bird (Eitan et al., 2014). Therefore, nowadays breeders are managed in a totally different way than decades ago, making comparison of results more difficult. Table 6. Fertility, hatchability, embryonic mortality, second grade chicks, chick weight, and chick production during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093    Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Expressed as percentage of total hatched chicks. View Large Table 6. Fertility, hatchability, embryonic mortality, second grade chicks, chick weight, and chick production during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093    Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Expressed as percentage of total hatched chicks. View Large During phase 3 (47 to 60 wk of age), hatchability of set eggs tended (P = 0.064) to be lower for the birds fed the CPl diet. These results are in contrary to the findings of Pearson and Herron (1981); Spratt and Leeson (1987), and Mohiti-Asli et al. (2012), who found no effect on hatchability. An opposite effect, thus an increased hatchability at lower daily CP intake, was found by Pearson and Herron (1982); Whitehead et al. (1985); Lopez and Leeson (1995a), and Van Emous et al. (2015b). It is suggested that the lower hatchability in the current study was caused by the low daily protein intake during phase 3 (17.8 g CP/d). Nowadays broiler breeder strains are much leaner than previous ones (Eitan et al., 2014) and maybe more sensitive to a lower daily protein intake. It is hypothesized that this is caused by the higher proportion of breast meat, which results in an increased protein turnover. This can result in an increased chance in deficiency of specific AA that are important for embryonic development. No effects of age at PS on incubation traits for the overall laying period were found, which is in agreement with Robinson et al. (1996), and Renema et al. (2001b) (Table 6), in the current study in phase 1 (22 or 24 to 34 wk of age); however, a higher fertility (P = 0.006) and a small tendency to a higher hatchability of set eggs (P = 0.093) was found for the early PS birds. It is noted that the effect of age at PS on fertility was more evident at 28 wk of age (+7.2%) than at 34 wk of age (+2.5%) (data not shown). The difference in fertility (and hatch of set eggs) can be explained by differences in body composition at sexual maturity (not measured) as previously suggested by Robinson et al. (1996). It is observed by Robinson et al. (1996) that early PS birds had an increased fat deposition between photo stimulation and first oviposition. In combination with the suggestion of Bornstein et al. (1984) that a minimum amount of fat is necessary for sexual maturation; this means that early PS birds mature earlier and are ready to produce fertile eggs. In the current study, chick weight was not affected by daily protein intake, consistent with the study of Mohiti-Asli et al. (2012) (Table 6). It is previously showed by Lopez and Leeson (1995a) that chick weight is not easily affected by protein intake. In their study, they found a decreased chick weight only at very low dietary protein content (10% CP; 14.5 g CP/d on average), whereas no effect was found for the 12, 14, and 16% CP diets. Chick weight in phase 1 originating of late PS breeders was highest (39.8 vs. 38.8 g), which resulted in a tendency (P = 0.087) to a higher overall chick weight (Table 6). It has been noted that the effect of age at PS on chick weight was much more pronounced at 28 (+1.6 g) than at 34 (+0.3 g) wk of age (data not shown). No other studies are available for comparison; however, it is likely that a higher initial egg weight, as found by Renema et al. (2001a), also results in a higher initial chick weight. The combination of the lower egg production and hatchability of set eggs in phase 3 resulted in a lower number of chicks (46.9 vs. 51.5) for the birds fed the CPl diet during that particularly phase of the laying period (Table 6). This result is in contrast with previous work (Whitehead et al., 1985) who found a higher chick production (+9.2) when birds were fed a 13.7 instead of a 16.8% CP diet. The difference between the current and the previous study is that in the current study, dietary CP level for the CPl birds was decreased from 13.5 to 11.5%, which is much lower than in the study of Whitehead et al. (1985), where dietary CP level for the low protein diet was maintained at 13.7% during the entire laying period. Chick production in phase 1 was increased (43.2 vs. 38.9) for early PS breeders resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks (150.5 vs. 142.8) (Table 6). This was mainly caused by the combination of the higher egg production (Table 5) and a tendency to a higher hatchability of set eggs during phase 1 (Table 6). As suggested before, the early PS birds were mature earlier, resulting in an earlier start of reproduction. In contrast to our results, Renema et al. (2001a) did not find an effect on chick production between 19 or 21 wk of age PS breeders. An opposite effect, however, was found by Robinson et al. (1996). A lower number of chicks was observed when breeders were PS at 120 and 130 d of age compared to 140, 150, or 160 d of age. They mentioned that this was due to a higher numerically number of embryonic mortality and numerically lower fertility. It is not clear what caused the differences between the current study and that of Robinson et al. (1996). It is therefore suggested that this is may be due to the extreme early age (17.0 and 18.5 wk of age) at PS in the latter study, resulting in a lower persistence of the birds. Progeny Performance Maternal CP diets did not affect production performance and slaughter yields of the progeny obtained of hatching eggs from 50 wk of age breeders (Table 7) which is in line with the results of Meija et al. (2013); Van Emous et al. (2015a), and Van Emous (2015). Contrary to the results of the current paper, Lopez and Leeson (1995c) found a decreased FCR (1.935 vs. 1.985) of the progeny from 52 wk of age breeders that were fed a 10 and 12% CP compared to a 14 and 16% diet. The absence of an effect of CP intake on progeny performance and slaughter yields might be explained by the fact that 60 to 70% of egg albumen lysine is derived from skeletal muscle reserves and the remainder from dietary resources (Ekmay, 2011). He suggested that skeletal muscles probably functioned as a transient protein pool from which lysine can be mobilized. Table 7. Performance and slaughter yields of male and female broilers (d 0 to 35) obtained of hatching eggs from 50 wk of age Ross 308 broiler breeders as affected by maternal dietary protein level (CP) and age at photo stimulation (PS). Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. View Large Table 7. Performance and slaughter yields of male and female broilers (d 0 to 35) obtained of hatching eggs from 50 wk of age Ross 308 broiler breeders as affected by maternal dietary protein level (CP) and age at photo stimulation (PS). Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. View Large Progeny from early PS breeders showed a significant lower FCR (1.473 vs. 1.491; P = 0.017) in the overall period of 0 to 35 d compared to broilers from late PS breeders (Table 7). A sound explanation for this phenomenon was not found. CONCLUSIONS Reducing dietary CP level by 15 g/kg compared to current breeder standards did not affect egg and chick production from 22 to 46 wk of production. However, egg and chick production during phase 3 was reduced for the birds fed an 11.5% CP diet without balancing for DEB. Chick production in phase 1 was higher for PSe birds, resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks. It is possible to decrease CP level of broiler breeder diets with comparable reproductive performance from 22 to 46 wk of age; however, this is questionable for phase 3 (47 to 60 wk of age). For maximal chick production early PS (21 vs. 23 wk of age) is recommended. ACKNOWLEDGMENTS This work was jointly supported by Evonik Nutrition & Care GmbH, Germany. The animal keepers of the poultry facilities Carus (Wageningen, the Netherlands) are thanked for their assistance in performing the study. The authors are grateful for the practical advices given by Gerwin van Ginkel while conducting the experiment. Thanks to René Kwakkel for helpful comments on the manuscript and to anonymous reviewers for providing useful comments on the draft manuscript. REFERENCES Aviagen-EPI. 2015. Management guide for Ross broiler breeders (in Dutch) . Roermond, The Netherlands. Bornstein S., Plavnik I., Lev Y.. 1984. Body weight and/or fatness as potential determinants of the onset of egg production in broiler breeder hens. Br. Poult. Sci.  25: 323– 341. Google Scholar CrossRef Search ADS PubMed  Ciacciariello M., Gous R. M.. 2005. A comparison of the effects of feeding treatments and lighting on age at first egg and subsequent laying performance and carcase composition of broiler breeder hens. Br. Poult. Sci.  46: 246– 254. Google Scholar CrossRef Search ADS PubMed  CVB. 2011. Feedstuffs table 2011 (In Dutch). Centraal Veevoederbureau  Lelystad, The Netherlands. De Beer M. 2009. Current approaches to feeding broiler breeders. Pages 104– 114 in Proc. 17th Eur. Symp. Poult. Nutr., Edinburgh, Scotland . World's Poult. Sci. Assoc., Attleborough, United Kingdom. Dos Santos T. T., Dos Santos S. A., Borges S. A., Da Silva A. V. F., Maiorka A.. 2011. Aplicação estratégica do balanço eletrolítico em dietas para matrizes pesadas. Cienc. Rural  41. 895– 900. Google Scholar CrossRef Search ADS   Eitan Y., Lipkin E., Soller M.. 2014. Body composition and reproductive performance at entry into lay of anno 1980 versus anno 2000 broiler breeder females under fast and slow release from feed restriction. Poult. Sci.  93: 1227– 1235. Google Scholar CrossRef Search ADS PubMed  Ekmay R. D. 2011. Protein utilization and requirements in broiler breeders . PhD Diss. University of Arkansas, Fayetteville, USA. Ekmay R. D., De Beer M., Mei S. J., Manangi M., Coon C. N.. 2013. Amino acid requirements of broiler breeders at peak production for egg mass, body weight, and fertility. Poult. Sci.  92: 992– 1006. Google Scholar CrossRef Search ADS PubMed  GenStat 18.1 Committee. 2015. Genstat 15 Reference Manual: Release 1 . Clarendon Press, Oxford, UK. Halley J., Cerrate S., Corzo A., Francher B. I.. 2016. Effect of altering dietary electrolyte balance using sodium bicarbonate and potassium carbonate on broiler breeder performance and egg shell parameters. Poult. Sci.  95( Suppl. 1): 94. (Abstr.) Havenstein G. B., Ferket P. R., Qureshi M. A.. 2003. Growth, livability, and feed conversion of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poult. Sci.  82: 1500– 1508. Google Scholar CrossRef Search ADS PubMed  Havenstein G. B., Ferket P. R., Qureshi M. A.. 2003. Carcass composition and yield of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poult. Sci.  82: 1509– 1518. Google Scholar CrossRef Search ADS PubMed  Joseph N. S., Robinson F. E., Korver D. R., Renema R. A.. 2000. Effect of dietary protein intake during the pullet-to-breeder transition period on early egg weight and production in broiler breeders. Poult. Sci.  79: 1790– 1796. Google Scholar CrossRef Search ADS PubMed  Joseph N. S., Dulaney A. A. J., Robinson F. E., Renema R. A., Zuidhof M. J.. 2002. The effects of age at photostimulation and dietary protein intake on reproductive efficiency in three strains of broiler breeders varying in breast yield. Poult. Sci.  81: 597– 607. Google Scholar CrossRef Search ADS PubMed  Keshavarz K., Nakajima S.. 1995. The effect of dietary manipulations of energy, protein, and fat during the growing and laying periods on early egg weight and egg components. Poult. Sci.  74: 50– 61. Google Scholar CrossRef Search ADS PubMed  Laughlin K. F. 2009. ‘ Breeder management: How did we get here?’. Pages 10– 25 in: Biology of Breeding Poultry . Poult. Sci. Series Vol. 29. Hocking P. M. ed. CABI. Wallingford, UK. Google Scholar CrossRef Search ADS   Lewis P. D. 2006. A review of lighting for broiler breeders. Br. Poult. Sci.  47: 393– 404. Google Scholar CrossRef Search ADS PubMed  Lilburn M. S., Myers-Miller D. J.. 1990. Effect of body weight, feed allowance, and dietary protein intake during the prebreeder period on early reproductive performance of broiler breeder hens. Poult. Sci.  69: 1118– 1125. Google Scholar CrossRef Search ADS PubMed  Lopez G., Leeson S.. 1995. Response of broiler breeders to low-protein diets: 1. Adult breeder performance. Poult. Sci.  74: 685– 695. Google Scholar CrossRef Search ADS PubMed  Lopez G., Leeson S.. 1995. Nitrogen content of manure from older broiler breeders fed varying quantities of crude protein. J. Appl. Poult. Res.  4: 390– 394. Google Scholar CrossRef Search ADS   Lopez G., Leeson S.. 1995. Response of broiler breeders to low-protein diets: 2. Offspring performance. Poult. Sci.  74: 696– 701. Google Scholar CrossRef Search ADS PubMed  Mejia L., McDaniel C. D., Corzo A.. 2012. Dietary influence of digestible lysine concentration on Cobb 500 hen broiler breeder reproductive performance. Poult. Sci.  91: 426– 431. Google Scholar CrossRef Search ADS PubMed  Mejia L., McDaniel C. D., Kidd M. T., Lopez K., Corzo A.. 2013. Evaluation of carryover effects of dietary lysine intake by Cobb 500 broiler breeder hens. Poult. Sci.  92: 709– 718. Google Scholar CrossRef Search ADS PubMed  Mohiti-Asli M., Shivazad M., Zaghari M., Rezaian M., Aminzadeh S., Mateos G. G.. 2012. Effects of feeding regimen, fiber inclusion, and crude protein content of the diet on performance and egg quality and hatchability of eggs of broiler breeder hens. Poult. Sci.  91: 3097– 3106. Google Scholar CrossRef Search ADS PubMed  Pearson R. A., Herron K. M.. 1981. Effects of energy and protein allowances during lay on the reproductive performance of broiler breeder hens. Br. Poult. Sci. Sci . 22: 227– 239. Google Scholar CrossRef Search ADS   Pearson R. A., Herron K. M.. 1982. Effects of maternal energy and protein intakes on the incidence of malformations and malpositions of the embryo and time of death during incubation. Br. Poult. Sci.  23: 71– 77. Google Scholar CrossRef Search ADS PubMed  Pishnamazi A., Renema R. A., Zuidhof M. J., Robinson F. E.. 2014. Effect of age at photostimulation on sexual maturation in broiler breeder pullets. Poult. Sci . 93: 1274– 1281. Google Scholar CrossRef Search ADS PubMed  Renema R. A., Robinson F. E., Goerzen P. R., Zuidhof M. J.. 2001. Effects of altering growth curve and age at photostimulation in female broiler breeders. 2. Egg production parameters. Can. J. Anim. Sci. Sci . 81: 477– 486. Google Scholar CrossRef Search ADS   Renema R. A., Robinson F. E., Goerzen P. R.. 2001. Effects of altering growth curve and age at photostimulation in female broiler breeders. 1. Reproductive development. Can. J. Anim. Sci.  81: 467– 476. Google Scholar CrossRef Search ADS   Renema R. A., Rustad M. E., Robinson F. E.. 2007. Implications of changes to commercial broiler and broiler breeder body weight targets over the past 30 years. World's Poult. Sci. J.  63: 457– 472. Google Scholar CrossRef Search ADS   Renema R. A., Moraes T. G. V., Zuidhof M. J.. 2013. Effects of broiler breeder nutrition on chick quality and broiler growth. Pages 212– 222 in Proc. 2nd Int. Poult. Meat Congress , Antalya, Turkey. Robinson F. E., Wautier T. A., Hardin R. T., Robinson N. A., Wilson J. L., Newcombe M., McKay R. I.. 1996. Effects of age at photostimulation on reproductive efficiency and carcass characteristics. 1. Broiler breeder hens. Can. J. Anim. Sci.  76: 275– 282. Google Scholar CrossRef Search ADS   Robinson F. E., Zuidhof M. J., Renema R. A.. 2007. Reproductive efficiency and metabolism of female broiler breeders as affected by genotype, feed allocation, and age at photostimulation. 1. Pullet growth and development. Poult. Sci.  86: 2256– 2266. Google Scholar CrossRef Search ADS PubMed  Spratt R. S., Leeson S.. 1987. Broiler breeder performance in response to diet protein and energy. Poult. Sci.  66: 683– 693. Google Scholar CrossRef Search ADS PubMed  Tona K., Onagbesan O., De Ketelaere B., Decuypere E., Bruggeman V.. 2004. Effects of Age of Broiler Breeders and Egg Storage on Egg Quality, Hatchability, Chick Quality, Chick Weight, and Chick Posthatch Growth to Forty-Two Days. J. Appl. Poult. Res.  13: 10– 18. Google Scholar CrossRef Search ADS   Van Emous R. A., Kwakkel R. P., van Krimpen M. M., van den Brand H., Hendriks W. H.. 2015a. Effects of growth patterns and dietary protein levels during rearing of broiler breeders on fertility, hatchability, embryonic mortality and offspring performance. Poult. Sci.  94: 681– 691. Google Scholar CrossRef Search ADS   Van Emous R. A. 2015. Body composition and reproduction in broiler breeders: impact of feeding strategies . PhD Diss. Wageningen University, Wageningen, the Netherlands. Van Emous R. A., Kwakkel R. P., van Krimpen M. M., Hendriks W. H.. 2015b. Effects of dietary protein levels during rearing and dietary energy levels during lay on body composition and reproduction in broiler breeder females. Poult. Sci.  94: 1030– 1042. Google Scholar CrossRef Search ADS   Whitehead C. C., Pearson R. A., Herron K. M., 1985. Biotin requirements of broiler breeders fed diets of different protein content and effect of insufficient biotin on the viability of progeny. Br. Poult. Sci.  26: 73– 82. Google Scholar CrossRef Search ADS PubMed  Yuan T., Lien R. J., McDaniel G. R.. 1994. Effects of increased rearing period body weights and early photostimulation on broiler breeder egg production. Poult. Sci.  73: 792– 800. Google Scholar CrossRef Search ADS PubMed  Zuidhof M. J., Schneider B. L., Carney V. L., Korver D. R., Robinson F. E.. 2014. Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005. Poult. Sci.  93: 2970– 2982. Google Scholar CrossRef Search ADS PubMed  © 2018 Poultry Science Association Inc. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Poultry Science Oxford University Press

Effects of dietary protein level and age at photo stimulation on reproduction traits of broiler breeders and progeny performance

Loading next page...
 
/lp/ou_press/effects-of-dietary-protein-level-and-age-at-photo-stimulation-on-YW9PgOE0Uf
Publisher
Oxford University Press
Copyright
© 2018 Poultry Science Association Inc.
ISSN
0032-5791
eISSN
1525-3171
D.O.I.
10.3382/ps/pey053
Publisher site
See Article on Publisher Site

Abstract

ABSTRACT A study with a 2 × 2 factorial arrangement was conducted to determine the effects of 2 dietary crude protein levels, high (CPh) or low (CPl), supplemented with free amino acids (AA), and 2 ages at photo stimulation (PS)—early (21 wk; PSe) or late (23 wk; PSl)—on reproduction traits of broiler breeders and progeny performance. Diets were isocaloric, and calculated CP content of the CPl diets was 15 g/kg lower than the CPh diets during all phases. A total of 480 female and 64 male Ross 308 breeders of 20 wk of age were used. Total egg production was similar between CPl and CPh birds during phase 1 and 2 but was reduced by 2.8 eggs for CPl birds during phase 3. For the overall laying period, CPl birds tended (P = 0.075) to produce 4.7 fewer total eggs. Hatchability of set eggs was similar between CPl and CPh birds during phases 1 and 2 but tended (P = 0.064) to be lower for CPl birds in phase 3. PSe birds showed an advanced age at sexual maturity and age at peak production of 4.6 and 5.3 d, respectively, resulting in 2.5 more total eggs during phase 1. During phase 1, PSe birds showed an almost 5% increased fertility. Chick production in phase 1 was higher for PSe birds resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks. Progeny from early PS breeders showed an overall significant lower feed conversion ratio (FCR). It was concluded that egg and chick production during phases 1 and 2 were not affected by dietary CP level, but egg and chick production was reduced for CPl birds during phase 3. On the other hand, PSe birds showed an increased number of chicks. It is possible to decrease CP level of breeder diets with comparable reproduction from 22 to 46 wk; however, this is questionable for phase 3. For maximal chick production, early PS is recommended. INTRODUCTION The last 5 to 6 decades have shown an increased genetic potential of broiler breeders for body weight gain due to selection of the progeny (Havenstein et al., 2003a, 2003b; Renema et al., 2007; Zuidhof et al., 2014). Although the poultry breeding companies have worked to maintain or even increase the rates of egg production and hatchability (Laughlin, 2009), achieving these potentials at the broiler breeder farm level on a consistent level has proven to be more challenging (Renema et al., 2013). Therefore, optimization of the diet (protein to energy ratio) and management is necessary to achieve maximal reproduction (Van Emous, 2015). It has been reported that feeding high levels of crude protein (CP), especially lysine, to broiler breeders will lead to over-fleshing (De Beer, 2009). This extra breast muscle requires energy input to prevent potential negative effects on lay persistency. Furthermore, Lopez and Leeson (1995a) clearly illustrated the negative effect of excess CP on fertility, and Ekmay et al. (2013) identified lysine and isoleucine as 2 amino acids (AA) directly affecting fertility in breeders. Pearson and Herron (1982) reported that low protein intake (21 vs. 27 g/d) improved hatchability due to a decreased embryonic mortality. An additional benefit of feeding breeders a low-CP diet is the decreased nitrogen excretion due to the lower nitrogen intake and higher nitrogen retention (Lopez and Leeson, 1995b). Feeding the breeders not only affects the breeders themselves but also the progeny (Zuidhof et al., 2014). However, relatively few papers are available on the effects of specific protein or AA intake of broiler breeders on offspring performance and slaughter yields (Lopez and Leeson, 1995c; Mejia et al., 2013; Van Emous et al., 2015a; Van Emous, 2015). Age at photo stimulation (PS) varies globally and may affect production performance of broiler breeders. In some regions, breeders are stimulated around 21 wk of age while in others, this is around 23 wk of age mainly due to the differences in threshold for minimal hatching egg size (minimum egg weights of 50 and 52 g, respectively). Most breeder farms currently delay age at PS until the flock is 21 to 23 wk of age (Joseph et al., 2002). Joseph et al. (2002) also stated that later PS breeders generally compensate for a later age at sexual maturity with an increased rate of lay. This was underlined by several authors who found no effect of age at PS on egg production during the overall laying period (Yuan et al., 1994; Robinson et al., 1996; Renema et al., 2001a; Joseph et al., 2002). No effects of age at PS on incubation traits were found in the studies of Robinson et al. (1996) and Renema et al. (2001a). In the study of Robinson et al. (1996), however, they found a higher chick production when birds were PS at 140, 150, or 160 d compared to 120 and 130 d. No literature is available on the effect of age at PS on progeny performance. As shown above, dietary CP level and age at PS can affect production performance of breeders. Most research, however, was carried out ∼15 years ago and modern broiler breeder strains differ genetically since that time (Havenstein et al., 2003a, 2003b; Renema et al., 2007; Zuidhof et al., 2014). Moreover, little is known about the combined effects of dietary CP level during lay and age at PS. Therefore, the objective of this study was to determine the effects of dietary CP levels during lay and age at PS on reproduction of Ross 308 broiler breeders and progeny performance. MATERIALS AND METHODS The protocol for the experiment conformed to the standards for animal experiments and was approved by the Ethical Committee of Wageningen UR, the Netherlands. Experimental Design The study was conducted as a 2 × 2 factorial completely randomized block design with 2 maternal dietary CP levels and 2 ages at PS. The birds received 2 diets with different levels of CP: high CP (CPh) at breeder recommendations, and low CP (CPl) (Table 1). Diets were formulated to be isocaloric (2,800 kcal/kg nitrogen corrected apparent metabolizable energy [AMEn]) and the calculated CP content of the CPl diets was 15 g/kg lower than the CPh diets during all phases (phase 1: respectively). Each phase had the following duration: phase 1: 22 or 24 to 34 wk of age (for early and late PS, respectively), phase 2: 35 to 46 wk of age, and phase 3: 47 to 60 wk of age. Experimental diets were formulated according to the recommendation of the breeder company and supplemented with free AA (Lys, Met, Thr, Trp, Arg, Ile, Val) (Aviagen-EPI, 2015). Breeders were reared (20 lx) at a photoperiod of 8L:16D (07:30 to 15:30) and photo-stimulated with 11 h of light (40 lx) at early (21 wk = PSe) or late age (23 wk = PSl). After PS, day length was gradually increased (22 or 24 wk of age = 12L:12D; 23 or 25 wk of age = 13L:11D; 24 or 26 wk of age = 13.5L:10.5D for PSe and PSl, respectively) to a photoperiod of 14L:10D at 25 (PSe) or 27 (PSl) wk of age. This was maintained until the end of the experiment at 60 wk of age, with light on from 0330 to 1730 h (40 lx). During the experiment, birds fed the different diets received the same daily amount of feed according to the growth pattern of the CPh diet. This resulted in a different daily nutrient intake (particularly CP and AA) for the CPl diet birds (Table 2). Table 1. Dietary ingredients, and analyzed and calculated nutrients of the breeder diets (g/kg, as-fed basis).   Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00    Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00  1Dietary protein level. CPh, high dietary protein level lay; CPl, low dietary protein level lay. 2Provided per kilogram of complete diet: vitamin A, 10,000 IU; vitamin D3, 1,500 IU; vitamin E, 100 mg; vitamin K3, 3.0 mg; vitamin B1, 3.0 mg; vitamin B2, 10.0 mg; vitamin B6, 4.0 mg; vitamin B12, 0.03 mg; niacinamide, 30 mg; D-pantothenic acid, 16.3 mg; choline chloride, 344 mg; folic acid, 2.0 mg; biotin, 0.3 mg; iron, 100 mg; copper, 15 mg; manganese, 100 mg; zinc, 100 mg; iodine, 2.0 mg; selenium, 0.15 mg. 3CVB matrix values (CVB, 2011) were used for diet formulation. View Large Table 1. Dietary ingredients, and analyzed and calculated nutrients of the breeder diets (g/kg, as-fed basis).   Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00    Pre breeder  Breeder 1 (22/24–34 wk)  Breeder 2 (35–46 wk)  Breeder 3 (47–60 wk)  Item    CPh1  CPl  CPh  CPl  CPh  CPl  Ingredient                Corn  683.6  650.0  665.7  660.0  694.4  685.2  719.1  Soybean meal, 48% CP  78.7  144.3  104.1  119.0  76.6  93.8  47.5  Sunflower meal  100.0  65.0  55.0  65.0  55.0  65.0  55.0  Wheat bran  96.0  36.5  69.6  45.0  65.0  45.0  68.6  Palm oil  2.0  1.2  –  8.0  1.1  7.3  –  Soya oil  –  15.1  14.5  9.5  9.8  7.1  7.4  Limestone  11.6  39.3  37.7  44.9  43.2  47.9  46.2  Chalk  10.0  30.0  32.0  30.0  32.0  30.0  32.0  Monocalcium phosphate  5.2  6.0  6.2  5.6  6.0  5.3  5.7  Salt  2.7  3.0  2.6  2.9  2.4  2.8  2.2  Sodium carbonate  2.7  2.3  2.9  2.4  3.1  2.6  3.4  Premix2  4.0  4.0  4.0  4.0  4.0  4.0  4.0  Curb  2.0  2.0  2.0  2.0  2.0  2.0  2.0  L-Lysine  0.7  0.1  1.4  0.4  1.8  0.8  2.3  DL-Methionine  0.8  1.2  1.6  1.2  1.6  1.1  1.5  L-Threonine  –  –  0.5  0.1  0.7  0.1  0.9  L-Tryptophan  –  –  –  –  0.1  –  0.2  L-Arginine  –  –  –  –  0.6  –  1.0  L-Isoleucine  –  –  0.2  –  0.5  –  0.7  L-Valine  –  –  –  –  0.1  –  0.3  Calculated content3                AMEn (kcal/kg)  2,800  2,800  2,800  2,800  2,800  2,800  2,800  CP  142.5  150.0  135.0  140.0  125.0  130.0  115.0  Dig. Lys  5.1  5.7  5.7  5.3  5.3  5.0  5.0  Dig. Met+Cys  5.1  5.5  5.5  5.2  5.2  4.9  4.9  Dig. Thr  4.2  4.6  4.5  4.3  4.3  4.0  4.0  Dig. Trp  1.4  1.5  1.3  1.4  1.2  1.3  1.2  Dig. Arg  8.2  8.8  7.6  8.1  7.3  7.4  6.9  Dig. Ile  4.8  5.4  4.8  4.9  4.6  4.5  4.3  Dig. Val  5.7  6.1  5.4  5.7  5.0  5.2  4.7  Dig. His  3.2  3.4  3.0  3.2  2.7  2.9  2.5  Dig. Phe  6.0  6.6  5.7  6.1  5.2  5.6  4.6  Dig. Gly  5.1  5.2  4.6  4.8  4.2  4.5  3.8  Dig. Ser  5.6  6.1  5.4  5.7  4.8  5.2  4.3  Na  1.8  1.8  1.8  1.8  1.8  1.8  1.8  K  7.0  7.0  6.4  6.6  5.9  6.1  5.3  Cl  2.3  2.3  2.3  2.3  2.3  2.3  2.3  Dietary electrolyte balance (mEq/kg)  192  192  178  182  163  169  150  Calcium  12.0  30.0  30.0  32.0  32.0  33.0  33.0  Total phosphorus  5.3  4.8  4.8  4.6  4.6  4.5  4.5  Available phosphorus  3.2  3.2  3.2  3.1  3.1  3.0  3.0  Linoleic acid  15.7  22.0  22.0  20.0  20.0  19.0  19.0  Analyzed content                CP  137.0  149.6  136.6  137.9  124.4  127.0  112.8  Lysine  6.33  6.78  6.82  6.16  6.17  6.04  5.93  Met+Cys  5.47  5.96  5.88  5.66  5.79  5.45  5.39  Threonine  4.99  5.51  5.42  5.18  5.12  4.81  4.77  Tryptophan  1.64  1.72  1.51  1.60  1.44  1.43  1.32  Arginine  9.01  9.90  8.76  9.00  8.09  8.28  7.50  Isoleucine  5.29  6.13  5.53  5.51  5.07  5.03  4.72  Leucine  11.71  13.23  11.94  12.09  10.76  11.43  9.98  Valine  6.60  7.22  6.45  6.59  5.78  6.14  5.47  Histidine  3.65  3.96  3.58  3.65  3.19  3.41  2.92  Phenylalanine  6.62  7.49  6.62  6.77  5.78  6.28  5.17  Glycine  6.46  6.65  5.95  6.12  5.30  5.75  4.86  Serine  6.52  7.23  6.37  6.48  5.61  6.04  5.00  1Dietary protein level. CPh, high dietary protein level lay; CPl, low dietary protein level lay. 2Provided per kilogram of complete diet: vitamin A, 10,000 IU; vitamin D3, 1,500 IU; vitamin E, 100 mg; vitamin K3, 3.0 mg; vitamin B1, 3.0 mg; vitamin B2, 10.0 mg; vitamin B6, 4.0 mg; vitamin B12, 0.03 mg; niacinamide, 30 mg; D-pantothenic acid, 16.3 mg; choline chloride, 344 mg; folic acid, 2.0 mg; biotin, 0.3 mg; iron, 100 mg; copper, 15 mg; manganese, 100 mg; zinc, 100 mg; iodine, 2.0 mg; selenium, 0.15 mg. 3CVB matrix values (CVB, 2011) were used for diet formulation. View Large Table 2. Daily crude protein (CP) and amino acid intake of broiler breeders from 21 to 60 wk of age.1 Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  1Values based on analyzed content of the diets. AA levels in the CPl diets were supplemented with free AA to the recommend level of the breeder company. 2FI, Feed intake. 3CPh, high dietary protein level lay; CPl, low dietary protein level lay. 4Values between parentheses are for the late PS birds. 5Weighted average of all weeks. View Large Table 2. Daily crude protein (CP) and amino acid intake of broiler breeders from 21 to 60 wk of age.1 Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  Age (wk)  FI 2  CP  Lysine  Methionine + Cystine  Threonine  Tryptophan  Isoleucine  Valine  Arginine      CPh3  CPl3  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl  CPh  CPl      < ![CDATA[ − − − − − − − − − ]] > g/bird/d < ![CDATA[ − − − − − − − − − ]] >  < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] > mg/bird/d < ![CDATA[ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − ]] >  21  105  14.39  14.39  665  665  574  574  524  524  172  172  555  555  693  693  946  946  22  110  15.07  15.07  696  696  602  602  549  549  180  180  582  582  726  726  991  991  23  118  17.65  16.12  800  805  703  694  650  640  203  178  723  653  852  761  1,168  1,034      (16.17)4  (16.17)  (747)  (747)  (645)  (645)  (589)  (589)  (194)  (194)  (624)  (624)  (779)  (779)  (1,063)  (1,063)  24  125  18.70  17.08  848  8.53  745  735  689  678  215  189  766  691  903  806  1,238  1,095      (17.13)  (17.13)  (791)  (791)  (684)  (684)  (624)  (624)  (205)  (205)  (661)  (661)  (825)  (825)  (1,126)  (1,126)  25  135  20.20  18.44  915  921  805  794  744  732  232  204  828  747  975  871  1,337  1,183  26  150  22.44  20.49  1017  1023  894  882  827  813  258  227  920  830  1,083  968  1,485  1,314  27  160  23.94  21.86  1,085  1,091  954  941  882  867  275  242  981  885  1,155  1,032  1,584  1,402  28–32  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  33  170  25.43  23.22  1,153  1,159  1,013  1,000  937  921  292  257  1,042  940  1,227  1,097  1,683  1,489  34  165  24.68  22.54  1,119  1,125  983  970  909  894  284  249  1,011  912  1,191  1,064  1,634  1,445  35–40  162  22.34  20.15  998  1,000  917  938  839  829  259  233  893  821  1,068  936  1,458  1,311  41–43  160  22.06  19.90  986  987  906  926  829  819  256  230  882  811  1,054  925  1,440  1,294  44–46  158  21.79  19.66  973  975  894  915  818  809  253  228  871  801  1,041  913  1,422  1,278  47–60  158  20.07  17.82  954  937  861  852  760  754  226  209  795  746  970  864  1,308  1,185  Average5  155  21.31  19.27  978  974  879  878  797  788  244  221  855  789  1026  914  1,397  1,257      (21.23)  (19.28)  (975)  (971)  (876)  (875)  (794)  (785)  (244)  (222)  (850)  (788)  (1,022)  (915)  (1,392)  (1,259)  1Values based on analyzed content of the diets. AA levels in the CPl diets were supplemented with free AA to the recommend level of the breeder company. 2FI, Feed intake. 3CPh, high dietary protein level lay; CPl, low dietary protein level lay. 4Values between parentheses are for the late PS birds. 5Weighted average of all weeks. View Large Housing and Management Breeders A total of 480 female and 64 male Ross 308 broiler breeders of 20 wk of age (PoultryPlus, Ambt Delden, The Netherlands) were used in this experiment. Breeders were fed during the pullet phase a commercial 4-phase feeding program (starter-1 diet: d 0 to 14, starter-2 diet: d 15 to 42; grower diet: d 43 to 105, pre-breeder diet: d 106 to 140). The starter-1, starter-2, grower, and pre-breeder diets contained 2,800, 2,800, 2,600, and 2,700 AMEn kcal/kg; 20.0, 17.0, 13.5, and 14.5% CP, respectively. The breeders were housed in 16 floor pens (1.8 × 4.0 m = 7.2 m2) with 34 birds (30 females and 4 males) per pen at the start of the laying period (20 wk of age) in 2 separated mechanically ventilated experimental broiler breeder rooms (8 pens per room). Between 20 and 27 wk of age, the 2 main rooms were divided in 2 different temporary light-tight compartments by wooden partitions. All 4 compartments were divided in 4 different pens, which resulted in total 16 pens. Each pen contained a laying nest, 2 feeding troughs for females (6 m length), a separate feeding pan for males, and 7 drink cups above the slatted plastic floor (1.8 × 1.0 m). The remaining area was bedded with wood shavings (2.0 kg/m2). Males received a commercial male diet (2,600 kcal/kg AMEn; 13.0% CP; 0.45% dig. Lys; 0.5% dig. M+C; 1.0% Ca; 0.3% aP). During the first 2 (PSe) or 4 (PSl) weeks birds received a standard pre-breeder diet according to the recommendation of the breeder company (Table 1). During the experiment, birds were maintained on the same target body weight (BW) and feed allocation was adjusted to the predetermined body growth curve during rearing and a combination of the predetermined body growth curve and egg production (Aviagen-EPI, 2015). Water was provided ad libitum and temperature was maintained at 20°C. Housing and Management Progeny A total of 384 1-day-old Ross 308 broiler chicks (192 female and 192 male) were used from hatching eggs of 50 wk of age for a growth trial from 0 to 35 d of age. After feather sexing, male and female chicks were randomly allotted to 32 floor pens (1.1 × 0.9 m), with 12 chicks (female or male) per pen. The broiler unit was illuminated continuously during the first 2 d and from d 3 onwards according to the schedule 18L:6D. A commercial 3-phase broiler feeding program (starter diet: d 0 to 11, grower diet: d 12 to 27, finisher diet: d 28 to 35) was provided to all chickens and feed and water were supplied ad libitum during the entire experimental period. The starter, grower and finisher diets contained 3,060, 3,180, and 3,225 AMEn kcal/kg; 22.3, 20,1, and 18.7% CP; 1.19, 1,06, and 0,96% dig. Lys; 0.88, 0,81, and 0,75% dig. M+C, respectively. Diets were formulated to meet or exceed the nutrient recommendations of the breeder company. Observations Body Weight To monitor BW and BW gain, 10 females (as group) and 1 male per pen were weighed weekly from 20 to 60 wk of age in the morning before feeding. At 20 and 60 wk of age, all birds per pen were weighed. Egg Weight, ASM and Peak Egg Production Egg weight of all hatching eggs (settable and small) of d 1 (Monday) were measured and recorded on a weekly basis. Average egg weight per phase was calculated. Age at sexual maturity (ASM) was defined as age at 50% production and was determined by a linear interpolation of the week (in days) where birds passed 50% rate of lay. Peak egg production was determined as a 3-wk rolling average. Egg Production All eggs per pen were collected, graded, and recorded daily. The total number of settable (above 50 g), small (under 50 g), double yolk, abnormal shell, dirty, and floor eggs were calculated per pen, per week and per feeding phase. Mortality Mortality was recorded daily per pen to calculate total percentage of mortality per week, feeding phase, and total laying period. Mortality was categorized as leg problems and other causes. Incubation Traits and Chick Production Incubation traits were measured at 28, 34, 40, 46, 50, and 56 wk of age. Per age, 150 eggs per pen from 6 to 9 d production period were transported and set, after an approximately 5- to 7-d storage period (16 to 18°C and 50 to 60% relative humidity), in an incubator at a commercial hatchery (Lagerwey, Lunteren, The Netherlands). At d 18, eggs were transferred to hatcher baskets and placed in an incubator. At d 21 of incubation, unhatched eggs were opened to determine stage of embryonic mortality. The following stages of embryonic mortality were used to classify the dead embryos: d 1 to 11 (early stage to feather follicle visible), d 12 to 17 (small embryo with feathers), d 18 to 21 (full grown dead embryo or live in shell). All chicks were graded as first- or second-grade chicks, wherein a first-grade chick was defined as dry, free of deformities, and bright eyes (Tona et al., 2004). BW of first-grade chicks were recorded. Fertility was calculated as the percentage of fertile eggs of the set eggs. Hatchability of set and fertile eggs was calculated as the percentage of all chicks hatched of set and fertile eggs, respectively. Embryonic mortality was calculated as a percentage of fertile eggs. Second-grade chicks were calculated as a percentage of total hatched chicks. Chick production was calculated using the mean hatchability of set eggs for each pen and multiplied by its settable egg number per phase and overall laying period. Progeny performance BW of the broilers in each pen was determined at d 0, 11, 27, and 35. Feed intake, BW gain, and feed conversion ratio (FCR) in each pen were recorded and calculated for the periods d 0 to 11, 12 to 27, 28 to 35, and 0 to 35. Mortality was recorded daily. Live weight, weight of carcass, wings, legs, back and breast meat were recorded at d 35 by slaughtering 4 birds (at random) per pen. Carcass yield was calculated as percentage of live weight of the broiler whereas wings, legs, back and breast meat were calculated as percentage of carcass weight. Statistical Analysis Raw data were analyzed for statistical outliers. Significant outliers (values deviating more than 2.5 times the standard deviation from the mean value) were not included in the data subjected to statistical analysis. The experimental data were analyzed using Genstat statistical software (Genstat, 2015). Statistical significance was declared at P ≤ 0.05, with 0.05 < P ≤ 0.10 considered as a tendency. Response parameters were analyzed using analysis of variance (ANOVA) according the following model: Yijk = μ + Blocki + CP dietj + Age at PSk + (CP diet * Age at PS)jk + εijk where Yijk was the dependent variable, μ was the overall mean, Blocki (4 compartments) was the random block effect (i = 1…4), CP dietj was the effect of CP diet (j = 1…2), Age at PSk was the effect of age at PS (k = 1…2), CP diet * Age at PSjk was the interaction effect between CP diet and age at PS and εijk was the residual error term. Pen was the experimental unit. The statistical model for progeny performance included sex (male and female). RESULTS AND DISCUSSION Body Weight A 9% lower total CP intake for the birds fed the CPl diet did not (except at 34 wk of age) affect BW of the birds during the laying period (Table 3). This was in line with data of previous studies of Pearson and Herron (1981); Lopez and Leeson (1995a); Joseph et al. (2000), and Mohiti-Asli et al. (2012). As suggested by several authors, BW of breeders seems to be more affected by energy than by protein intake per se (Pearson and Herron, 1981; Spratt and Leeson, 1987; Keshavarz and Nakajima, 1995; Mohiti-Asli et al., 2012). Table 3. Body weight (g) at 20, 24, 34, 46 and 60 wk of age as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. View Large Table 3. Body weight (g) at 20, 24, 34, 46 and 60 wk of age as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  Item1  20 wk  24 wk  34 wk  46 wk  60 wk  CP level            CPh  2,388  2,972  3,585a  3,704  3,830  CPl  2,387  2,931  3,482b  3,662  3,702  Age at PS            PSe  2,375  2,966  3,506  3,652  3,753  PSl  2,400  2,937  3,561  3,713  3,780  SEM  15.9  22.3  20.9  36.3  75.3  P-value            CP  0.99  0.22  0.005  0.43  0.26  PS  0.29  0.38  0.088  0.26  0.81  CP × PS  0.38  0.91  0.54  0.34  0.41  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. View Large Concurring with previous research of Robinson et al. (2007), no effects of different PS on BW were observed at onset of lay (20 and 24 wk of age) (Table 3). Egg Weight, ASM, and Peak Egg Production Daily CP intake did not affect overall egg weight (Table 4), consistent with the studies of Pearson and Herron (1981); Joseph et al. (2002); Mohiti-Asli et al. (2012), and Van Emous et al. (2015b; between 22 and 45 wk of age). In the study from Van Emous et al. (2015b) daily CP intake of 20.5, 22.0 or 23.5 g/d did not affect egg weight during the first phase of lay; however, during the second phase of lay breeders fed 19.4 g/d CP daily showed a lower egg weight than breeders fed 21.5 g/d. In the previous mentioned studies of Pearson and Herron (1981); Joseph et al. (2000); Mohiti-Asli et al. (2012), and Van Emous et al. (2015b), breeders on the lowest daily CP intake received 21.3, 20.8, 25.7 and 20.5 g/d, respectively. Table 4. Egg weight, ASM, peak egg production, and age at peak egg production as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42    Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Egg weight was determined for all hatching eggs (small and settable). 3ASM, age at sexual maturity, defined as age at 50% production. 4Determined as a 3-wk rolling average of %hen d. View Large Table 4. Egg weight, ASM, peak egg production, and age at peak egg production as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42    Egg weight  Egg weight  Egg weight  Egg weight  ASM3 (d)  Peak egg  Age at peak    phase 12 (g)  phase 2 (g)  phase 3 (g)  laying period (g)    production  egg production  Item1            (%)4  (d)  CP level                CPh  57.1  64.3  70.1  64.6  180.5  90.7  206.5  CPl  56.9  64.2  70.6  64.7  181.1  91.7  210.0  Age at PS                PSe  56.9  64.5  70.6  64.8  178.5b  90.4  205.6b  PSl  57.1  64.1  70.0  64.5  183.1a  92.0  210.9a  SEM  0.14  0.34  0.28  0.24  0.28  0.64  1.48  P-value                CP  0.22  0.92  0.25  0.77  0.15  0.31  0.12  PS  0.40  0.43  0.20  0.41  <0.001  0.11  0.029  CP × PS  0.67  0.58  0.95  0.73  0.21  0.53  0.42  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Egg weight was determined for all hatching eggs (small and settable). 3ASM, age at sexual maturity, defined as age at 50% production. 4Determined as a 3-wk rolling average of %hen d. View Large Egg weight during the overall laying period was not affected by age at PS (Table 4), which was consistent with previous studies (Yuan et al., 1994; Robinson et al., 1996; Renema et al., 2001a; Pishnamazi et al., 2014). Contrary to our results, Joseph et al. (2000, 2002) found that birds that were photo stimulated at 23 versus 21 wk of age produced heavier eggs throughout the overall laying period. They postulated that this was mainly caused by a higher BW during the first part or overall laying period. In the current study no effect on BW during the initial and overall laying period was observed which explained the absence of differences in egg weight. Age at sexual maturity was not affected by differences in daily CP intake (Table 4) which concurred with studies of Pearson and Herron (1981); Spratt and Leeson (1987); Lopez and Leeson (1995a), and Joseph et al. (2000). Contrary to those findings, Van Emous et al. (2015b) observed a delayed ASM of 1.4 d when breeders received a 10% higher daily CP intake during initial lay. In the latter study, however, an opposite advanced peak egg production of 8.5 d was found. They postulate that this was caused by the higher daily CP intake which stimulates the development of the reproductive tract (Lilburn and Myers-Miller, 1990). The reason for the absence of an effect on ASM in the current study, may be due to the fact that the difference in daily CP intake (21.3 vs. 19.3 g/d) between the treatments was not distinctive enough. Late PS birds showed a delayed ASM (P < 0.001) and age at egg peak production (P = 0.029) of 4.6 and 5.3 d, respectively (Table 4). Age at sexual maturity, in the current study, was delayed by 0.33 d per d that PS was delayed. This was in close agreement with Renema et al. (2001b), and Pishnamazi et al. (2014) who found an increase of 0.35 and 0.40 d, respectively, per d that PS was delayed. A maturation rate of 0.36 d per d that PS was delayed was calculated by Lewis (2006). Robinson et al. (1996); Joseph et al. (2002), and Ciacciariello and Gous (2005) found lower maturation rates of 0.22, 0.27, and 0.21 d, respectively, per day that PS was delayed. Neither peak egg production and age at peak egg production were influenced in the current study by daily CP intake (Table 4). This is consistent with Spratt and Leeson (1987), but in contrast with Lopez and Leeson (1995a). The latter authors reported that birds fed a 16% CP diet reached the highest and the most persistent peak production. However, due to a difference in persistency in the second part of lay, no effect on total egg production at the end of lay was observed in that study. No effect of age at PS on peak egg production was found in the current study (Table 4). In the literature, only 1 study (Yuan et al., 1994) is available that shows some information about peak egg production. Yuan et al. (1994) found that breeders PS at 14 and 17 wk of age showed a higher number of early egg production (until 30 wk of age) and a lower peak egg production compared to breeders PS at 20 wk of age. The difference between the current and the study of Yuan et al. (1994) is that the latter authors applied extreme early ages at PS (14 and 17 wk of age), which is not relevant under practical circumstances. Egg Production Reductions of 15 g/kg of dietary CP levels during phase 1 (22 or 24 to 34 wk of age) and phase 2 (35 to 46 wk of age) did not affect total egg production and settable eggs compared to the CPh diet (Table 5). In phase 3 (47 to 60 wk of age), reductions of CP levels from 13.0 to 11.5% reduced (P = 0.043) total egg production. This resulted in a tendency (P = 0.075) to a lower total egg production (183.5 vs. 188.2 eggs/hen housed) for the overall laying period (22 or 24 to 60 wk of age) for birds fed the CPl diet (19.3 g CP/bird/d). In contrast with the current study, Pearson and Herron (1981); Spratt and Leeson (1987), and Lopez and Leeson (1995a) found no effects on egg production when birds were fed a low daily CP intake (21.3, 16.9 and 14.9 g CP/bird, respectively). An opposite effect was reported by Whitehead et al. (1985); who found a higher egg production when breeders were fed a lower daily protein intake (20.5 vs. 25.2 g CP/bird). Joseph et al. (2000) found a lower numerical egg production for birds fed 14 compared to 16 and 18% CP diets; however, they carried out the experiment between 24 and 29 wk of age. The difference in effect on egg production due to the different daily protein intake in phase 3 in the current study might be explained by a low dietary electrolyte balance (DEB) level of the CPl diet. To achieve an 11.5% CP diet, a very low level of soybean meal was used, which resulted in a K content of 5.3 g/kg and a DEB of 150 mEq/kg. Dos Santos et al. (2011) reported that broiler breeders from 55 to 66 wk of age had decreased egg production when fed diets with a DEB of 150 mEq/kg compared to 180 mEq/kg. Recent research of Halley et al. (2016), using Ross 708 broiler breeders, reported that levels of 180 and 205 mEq/kg analyzed DEB significantly improved egg production in wk 50 compared to breeders fed a diet with 160 mEq/kg. The severe reduction in DEB during phase 3 for the CPl diet in the current study may have been involved with the reduction in egg production during this phase. Table 5. Egg production traits and defective egg production (n/hen) during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Settable eggs, normal egg ≥ 50 g. 3Small eggs, normal egg < 50 g. 4Abnormal shell eggs, cracked, soft shell and shell less eggs. 5Floor eggs, eggs laid outside nests (in litter or on slats). View Large Table 5. Egg production traits and defective egg production (n/hen) during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders. Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  Item1  Total eggs  Settable eggs2  Small eggs3  Double yolk  Abnormal shell  Dirty eggs  Floor eggs5          eggs  eggs4            Phase 1 (22 or 24 to 34 wk of age)        CP level                CPh  55.2  48.9  2.2  0.9  0.4  0.9b  1.9  CPl  54.6  48.1  2.3  0.8  0.5  1.4a  1.5  Age at PS                PSe  56.2a  49.8a  2.7a  0.9  0.6  1.1  1.1b  PSl  53.7b  47.2b  1.8b  0.8  0.4  1.2  2.3a  SEM  0.54  0.67  0.19  0.10  0.07  0.08  0.28  P-value                CP  0.44  0.44  0.78  0.30  0.33  0.001  0.41  PS  0.007  0.020  0.007  0.28  0.14  0.26  0.016  CP × PS  0.30  0.70  0.60  0.23  0.12  0.59  0.95        Phase 2 (35 to 46 wk of age)        CP level                CPh  68.3  65.0  0.1  0.2  0.6  0.6  1.9  CPl  67.0  63.3  0.1  0.2  1.0  0.6  1.9  Age at PS                PSe  67.6  64.8  0.1  0.2  0.8  0.6  1.2  PSl  67.7  63.5  0.1  0.2  0.8  0.6  2.6  SEM  0.54  0.70  0.02  0.03  0.14  0.11  0.55  P-value                CP  0.11  0.11  0.95  0.86  0.068  0.98  0.97  PS  0.90  0.19  0.46  0.39  0.89  0.78  0.092  CP × PS  0.65  0.27  0.29  0.19  0.89  0.32  0.31        Phase 3 (47 to 60 wk of age)        CP level                CPh  64.7a  61.1  0.0  0.1b  0.5b  0.6  2.4  CPl  61.9b  58.1  0.0  0.3a  0.9a  0.5  2.2  Age at PS                PSe  63.5  60.4  0.0  0.2  0.7  0.7  1.6  PSl  63.0  58.7  0.0  0.2  0.7  0.4  3.0  SEM  0.86  1.10  0.01  0.07  0.09  0.11  0.72  P-value                CP  0.043  0.082  0.69  0.047  0.013  0.49  0.79  PS  0.67  0.29  0.13  0.89  0.93  0.13  0.17  CP × PS  0.20  0.085  0.15  0.52  0.83  0.75  0.25        Laying period (22 or 24 to 60 wk of age)        CP level                CPh  188.2  174.9  2.3  1.2  1.5a  2.1  6.2  CPl  183.5  169.5  2.3  1.3  2.3b  2.5  5.5  Age at PS                PSe  187.3  175.0  2.8a  1.3  2.0  2.3  3.8  PSl  184.4  169.3  1.9b  1.2  1.8  2.3  7.9  SEM  1.69  2.27  0.18  0.14  0.24  0.20  1.44  P-value                CP  0.075  0.12  0.78  0.67  0.028  0.24  0.76  PS  0.24  0.10  0.006  0.53  0.58  0.78  0.074  CP × PS  0.26  0.19  0.70  0.84  0.75  0.60  0.34  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Settable eggs, normal egg ≥ 50 g. 3Small eggs, normal egg < 50 g. 4Abnormal shell eggs, cracked, soft shell and shell less eggs. 5Floor eggs, eggs laid outside nests (in litter or on slats). View Large A higher number (2.3 vs. 1.5%) of abnormal-shell eggs (cracked, soft shell, and shell-less) during the overall laying period were found for birds fed the CPl diet (P = 0.028), which was mainly caused by the higher number of abnormal-shell eggs in phase 3 of lay (Table 5). Possible dietary factors that affect eggshell quality are calcium intake, available phosphorus intake, and ingredients. In the current study, all these factors were equal, and therefore it is hypothesized that the low level of DEB may have been related with the increased number of abnormal-shell eggs in the CPl group. In the current study, early PS birds produced in the first phase 2.5 more total, 2.6 more settable, 0.9 more small, and 1.2 fewer floor eggs (Table 5). Egg production during the overall laying period, however, was not affected by age at PS. This result for the overall laying period was previously found by Yuan et al. (1994); Robinson et al. (1996); Renema et al. (2001a), and Joseph et al. (2002). The latter authors stated that later PS breeders generally compensate for a later age at sexual maturity with an increased rate of lay. Not surprisingly, the early PS birds in the current study produced more small eggs (2.7 vs. 1.8) during phase 1. In a previous study of Renema et al. (2001a) initial egg weight was decreased (43.9 vs. 46.0 g) for early PS breeders (19 vs. 21 wk of age). This difference in egg weight was caused by the 4.9 d earlier age at sexual maturity, lower BW at onset of lay (2,547 vs. 2,681 g) of the breeders, and an 11.5% lower liver weight of early PS birds, which limits the production of yolk precursors and thus also egg weight (Renema et al., 2001b). Mortality No effect of different daily CP intake was found on mortality (data not shown), which is contrary to Lopez and Leeson (1995a) who found a trend to a lower mortality when birds were fed a 10% CP diet. An opposite effect was shown by Van Emous et al. (2015b) who found an increased mortality during the first phase of lay (22 to 45 wk of age) for birds fed the lowest daily CP intake. The majority of the mortality was due to an increased incidence of ruptures of the gastrocnemius tendons. They hypothesized that this was caused by competitive feeding behavior resulting in (hyper)activity like running and jumping, inducing a higher risk of damaging the tendons. This competitive feeding behavior was avoided by additional feeding space in the current study. Incubation Traits and Chick Production In the current study, fertility was not affected by differences in daily CP intake (Table 6), which was also reported by Whitehead et al. (1985); Mejia et al. (2012), and Van Emous et al. (2015b). Other studies, however, showed that feeding broiler breeders a high daily protein level during the laying period resulted in decreased fertility (Lopez and Leeson, 1995a; Ekmay et al., 2013). It is not clear what caused the differences between the current and latter cited studies, but possible causative factors are: housing system, breed, amount of feed, energy to protein ratio, and energy level. Moreover, body composition of broiler breeders has changed dramatically during the last decades to a much leaner bird (Eitan et al., 2014). Therefore, nowadays breeders are managed in a totally different way than decades ago, making comparison of results more difficult. Table 6. Fertility, hatchability, embryonic mortality, second grade chicks, chick weight, and chick production during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093    Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Expressed as percentage of total hatched chicks. View Large Table 6. Fertility, hatchability, embryonic mortality, second grade chicks, chick weight, and chick production during the 3 phases of the laying period and overall laying period as affected by dietary protein level (CP) and age at photo stimulation (PS) of Ross 308 broiler breeders.   Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093    Fertility (%)  Hatch. of set  Hatch. of  Embryonic mortality of fertile eggs  2nd grade  Chick  Chick  Item1    eggs (%)  fertile eggs  (%)  chicks (%)2  weight (g)  production        (%)  1 to 11 d  12 to 17 d  18 to 21 d      (#)      Phase 1 (22 or 24 to 34 wk of age)        CP level                    CPh  91.1  84.2  92.7  3.9  1.0  2.4  0.7  39.3  41.2  CPl  91.1  84.9  93.5  3.3  0.9  2.3  0.8  39.2  40.9  Age at PS                    PSe  93.5a  86.8  93.1  3.2  1.2  2.6  0.5  38.8b  43.2a  PSl  88.6b  82.3  93.1  3.9  0.8  2.2  1.0  39.8a  38.9b  SEM  1.14  1.72  0.97  0.57  0.23  0.46  0.42  0.31  1.19  P-value                    CP  0.99  0.79  0.54  0.50  0.70  0.78  0.80  0.91  0.85  PS  0.006  0.093  0.95  0.40  0.19  0.55  0.20  0.019  0.026  CP × PS  0.56  0.64  0.83  0.57  0.77  0.31  0.82  0.44  0.59      Phase 2 (35 to 46 wk of age)        CP level                    CPh  92.9  88.0  94.9  2.3  0.9  1.7  0.7  43.6  57.1  CPl  93.4  88.5  95.3  1.8  0.8  2.1  0.3  43.5  56.0  Age at PS                    PSe  94.3  88.8  94.4  2.2  0.8  2.3  0.4  43.4  57.5  PSl  92.0  87.7  95.7  1.9  0.9  1.4  0.5  43.6  55.6  SEM  2.10  2.59  0.79  0.28  0.17  0.49  0.15  0.17  1.30  P-value                    CP  0.79  0.84  0.70  0.24  0.70  0.58  0.11  0.80  0.51  PS  0.27  0.66  0.28  0.48  0.65  0.22  0.68  0.41  0.27  CP × PS  0.50  0.18  0.085  0.12  0.015  0.36  0.99  0.70  0.073      Phase 3 (47 to 60 wk of age)        CP level                    CPh  90.3  84.4  94.8  2.0  1.7  1.6  1.2  46.3  51.5a  CPl  88.5  80.9  93.3  3.0  1.8  1.9  1.8  46.5  46.9b  Age at PS                    PSe  88.7  82.4  94.6  2.4  1.5  1.5  1.6  46.3  49.8  PSl  90.1  82.8  93.4  2.6  2.1  2.0  1.4  46.5  48.6  SEM  1.42  1.21  0.88  0.41  0.47  0.32  0.46  0.17  0.94  P-value                    CP  0.38  0.064  0.18  0.13  0.85  0.42  0.33  0.41  0.005  PS  0.51  0.81  0.28  0.83  0.37  0.35  0.80  0.54  0.40  CP × PS  0.96  0.51  0.40  0.032  0.92  0.35  0.31  0.11  0.038        Laying period (22 or 24 to 60 wk of age)          CP level                    CPh  91.4  85.5  94.1  2.7  1.2  1.9  0.9  43.0  149.6  CPl  91.0  84.8  94.0  2.7  1.2  2.1  1.0  43.1  143.7  Age at PS                    PSe  92.2  86.0  94.0  2.6  1.2  2.1  0.8  42.8  150.5  PSl  90.2  84.3  94.1  2.8  1.2  1.9  1.0  43.3  142.8  SEM  0.95  1.21  0.76  0.34  0.24  0.36  0.20  0.17  2.80  P-value                    CP  0.76  0.66  0.94  0.96  0.90  0.71  0.60  0.90  0.16  PS  0.18  0.34  0.97  0.71  0.72  0.58  0.56  0.087  0.071  CP × PS  0.55  0.29  0.32  0.30  0.31  0.56  0.30  0.41  0.093  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. Each value represents the mean of 8 replicate pens. 2Expressed as percentage of total hatched chicks. View Large During phase 3 (47 to 60 wk of age), hatchability of set eggs tended (P = 0.064) to be lower for the birds fed the CPl diet. These results are in contrary to the findings of Pearson and Herron (1981); Spratt and Leeson (1987), and Mohiti-Asli et al. (2012), who found no effect on hatchability. An opposite effect, thus an increased hatchability at lower daily CP intake, was found by Pearson and Herron (1982); Whitehead et al. (1985); Lopez and Leeson (1995a), and Van Emous et al. (2015b). It is suggested that the lower hatchability in the current study was caused by the low daily protein intake during phase 3 (17.8 g CP/d). Nowadays broiler breeder strains are much leaner than previous ones (Eitan et al., 2014) and maybe more sensitive to a lower daily protein intake. It is hypothesized that this is caused by the higher proportion of breast meat, which results in an increased protein turnover. This can result in an increased chance in deficiency of specific AA that are important for embryonic development. No effects of age at PS on incubation traits for the overall laying period were found, which is in agreement with Robinson et al. (1996), and Renema et al. (2001b) (Table 6), in the current study in phase 1 (22 or 24 to 34 wk of age); however, a higher fertility (P = 0.006) and a small tendency to a higher hatchability of set eggs (P = 0.093) was found for the early PS birds. It is noted that the effect of age at PS on fertility was more evident at 28 wk of age (+7.2%) than at 34 wk of age (+2.5%) (data not shown). The difference in fertility (and hatch of set eggs) can be explained by differences in body composition at sexual maturity (not measured) as previously suggested by Robinson et al. (1996). It is observed by Robinson et al. (1996) that early PS birds had an increased fat deposition between photo stimulation and first oviposition. In combination with the suggestion of Bornstein et al. (1984) that a minimum amount of fat is necessary for sexual maturation; this means that early PS birds mature earlier and are ready to produce fertile eggs. In the current study, chick weight was not affected by daily protein intake, consistent with the study of Mohiti-Asli et al. (2012) (Table 6). It is previously showed by Lopez and Leeson (1995a) that chick weight is not easily affected by protein intake. In their study, they found a decreased chick weight only at very low dietary protein content (10% CP; 14.5 g CP/d on average), whereas no effect was found for the 12, 14, and 16% CP diets. Chick weight in phase 1 originating of late PS breeders was highest (39.8 vs. 38.8 g), which resulted in a tendency (P = 0.087) to a higher overall chick weight (Table 6). It has been noted that the effect of age at PS on chick weight was much more pronounced at 28 (+1.6 g) than at 34 (+0.3 g) wk of age (data not shown). No other studies are available for comparison; however, it is likely that a higher initial egg weight, as found by Renema et al. (2001a), also results in a higher initial chick weight. The combination of the lower egg production and hatchability of set eggs in phase 3 resulted in a lower number of chicks (46.9 vs. 51.5) for the birds fed the CPl diet during that particularly phase of the laying period (Table 6). This result is in contrast with previous work (Whitehead et al., 1985) who found a higher chick production (+9.2) when birds were fed a 13.7 instead of a 16.8% CP diet. The difference between the current and the previous study is that in the current study, dietary CP level for the CPl birds was decreased from 13.5 to 11.5%, which is much lower than in the study of Whitehead et al. (1985), where dietary CP level for the low protein diet was maintained at 13.7% during the entire laying period. Chick production in phase 1 was increased (43.2 vs. 38.9) for early PS breeders resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks (150.5 vs. 142.8) (Table 6). This was mainly caused by the combination of the higher egg production (Table 5) and a tendency to a higher hatchability of set eggs during phase 1 (Table 6). As suggested before, the early PS birds were mature earlier, resulting in an earlier start of reproduction. In contrast to our results, Renema et al. (2001a) did not find an effect on chick production between 19 or 21 wk of age PS breeders. An opposite effect, however, was found by Robinson et al. (1996). A lower number of chicks was observed when breeders were PS at 120 and 130 d of age compared to 140, 150, or 160 d of age. They mentioned that this was due to a higher numerically number of embryonic mortality and numerically lower fertility. It is not clear what caused the differences between the current study and that of Robinson et al. (1996). It is therefore suggested that this is may be due to the extreme early age (17.0 and 18.5 wk of age) at PS in the latter study, resulting in a lower persistence of the birds. Progeny Performance Maternal CP diets did not affect production performance and slaughter yields of the progeny obtained of hatching eggs from 50 wk of age breeders (Table 7) which is in line with the results of Meija et al. (2013); Van Emous et al. (2015a), and Van Emous (2015). Contrary to the results of the current paper, Lopez and Leeson (1995c) found a decreased FCR (1.935 vs. 1.985) of the progeny from 52 wk of age breeders that were fed a 10 and 12% CP compared to a 14 and 16% diet. The absence of an effect of CP intake on progeny performance and slaughter yields might be explained by the fact that 60 to 70% of egg albumen lysine is derived from skeletal muscle reserves and the remainder from dietary resources (Ekmay, 2011). He suggested that skeletal muscles probably functioned as a transient protein pool from which lysine can be mobilized. Table 7. Performance and slaughter yields of male and female broilers (d 0 to 35) obtained of hatching eggs from 50 wk of age Ross 308 broiler breeders as affected by maternal dietary protein level (CP) and age at photo stimulation (PS). Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. View Large Table 7. Performance and slaughter yields of male and female broilers (d 0 to 35) obtained of hatching eggs from 50 wk of age Ross 308 broiler breeders as affected by maternal dietary protein level (CP) and age at photo stimulation (PS). Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  Item1  BW gain (g/bird/d)  Feed intake (g/bird/d)  FCR (g/g)  Mortality (%)  Carcass (% BW)  Legs (% carcass)  Breast meat (% carcass)  CP level                CPh  70.6  104.5  1.483  1.1  68.4  32.3  34.2  CPl  71.1  105.0  1.481  1.9  68.2  32.0  34.4  Age at PS                PSe  70.8  104.2  1.473b  2.5  68.2  32.2  34.4  PSl  70.8  105.4  1.491a  0.6  68.4  32.1  34.2  Sex                Female  64.3  97.5  1.517  1.1  68.7  32.0  34.6  Male  77.4  112.0  1.447  1.9  68.0  32.3  34.1  SEM  21.3  0.89  0.0047  1.08  0.19  0.22  0.29  P-value                CP  0.64  0.70  0.74  0.61  0.51  0.45  0.77  PS  0.99  0.35  0.017  0.24  0.47  0.86  0.60  Sex  <0.001  <0.001  <0.001  0.61  0.017  0.27  0.24  CP × PS  0.61  0.57  0.016  0.20  0.21  0.98  0.84  CP × Sex  0.67  0.38  0.22  0.056  0.95  0.66  0.69  PS × Sex  0.81  0.99  0.43  0.20  0.75  0.48  0.57  CP × PS × Sex  0.79  0.43  0.015  0.24  0.29  0.61  0.70  a,bMeans within a column with no common superscript differ (P ≤ 0.05). 1CPh, high dietary protein level lay; CPl, low dietary protein level lay; PSe, early photo stimulation; PSl, late photo stimulation. View Large Progeny from early PS breeders showed a significant lower FCR (1.473 vs. 1.491; P = 0.017) in the overall period of 0 to 35 d compared to broilers from late PS breeders (Table 7). A sound explanation for this phenomenon was not found. CONCLUSIONS Reducing dietary CP level by 15 g/kg compared to current breeder standards did not affect egg and chick production from 22 to 46 wk of production. However, egg and chick production during phase 3 was reduced for the birds fed an 11.5% CP diet without balancing for DEB. Chick production in phase 1 was higher for PSe birds, resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks. It is possible to decrease CP level of broiler breeder diets with comparable reproductive performance from 22 to 46 wk of age; however, this is questionable for phase 3 (47 to 60 wk of age). For maximal chick production early PS (21 vs. 23 wk of age) is recommended. ACKNOWLEDGMENTS This work was jointly supported by Evonik Nutrition & Care GmbH, Germany. The animal keepers of the poultry facilities Carus (Wageningen, the Netherlands) are thanked for their assistance in performing the study. The authors are grateful for the practical advices given by Gerwin van Ginkel while conducting the experiment. Thanks to René Kwakkel for helpful comments on the manuscript and to anonymous reviewers for providing useful comments on the draft manuscript. REFERENCES Aviagen-EPI. 2015. Management guide for Ross broiler breeders (in Dutch) . Roermond, The Netherlands. Bornstein S., Plavnik I., Lev Y.. 1984. Body weight and/or fatness as potential determinants of the onset of egg production in broiler breeder hens. Br. Poult. Sci.  25: 323– 341. Google Scholar CrossRef Search ADS PubMed  Ciacciariello M., Gous R. M.. 2005. A comparison of the effects of feeding treatments and lighting on age at first egg and subsequent laying performance and carcase composition of broiler breeder hens. Br. Poult. Sci.  46: 246– 254. Google Scholar CrossRef Search ADS PubMed  CVB. 2011. Feedstuffs table 2011 (In Dutch). Centraal Veevoederbureau  Lelystad, The Netherlands. De Beer M. 2009. Current approaches to feeding broiler breeders. Pages 104– 114 in Proc. 17th Eur. Symp. Poult. Nutr., Edinburgh, Scotland . World's Poult. Sci. Assoc., Attleborough, United Kingdom. Dos Santos T. T., Dos Santos S. A., Borges S. A., Da Silva A. V. F., Maiorka A.. 2011. Aplicação estratégica do balanço eletrolítico em dietas para matrizes pesadas. Cienc. Rural  41. 895– 900. Google Scholar CrossRef Search ADS   Eitan Y., Lipkin E., Soller M.. 2014. Body composition and reproductive performance at entry into lay of anno 1980 versus anno 2000 broiler breeder females under fast and slow release from feed restriction. Poult. Sci.  93: 1227– 1235. Google Scholar CrossRef Search ADS PubMed  Ekmay R. D. 2011. Protein utilization and requirements in broiler breeders . PhD Diss. University of Arkansas, Fayetteville, USA. Ekmay R. D., De Beer M., Mei S. J., Manangi M., Coon C. N.. 2013. Amino acid requirements of broiler breeders at peak production for egg mass, body weight, and fertility. Poult. Sci.  92: 992– 1006. Google Scholar CrossRef Search ADS PubMed  GenStat 18.1 Committee. 2015. Genstat 15 Reference Manual: Release 1 . Clarendon Press, Oxford, UK. Halley J., Cerrate S., Corzo A., Francher B. I.. 2016. Effect of altering dietary electrolyte balance using sodium bicarbonate and potassium carbonate on broiler breeder performance and egg shell parameters. Poult. Sci.  95( Suppl. 1): 94. (Abstr.) Havenstein G. B., Ferket P. R., Qureshi M. A.. 2003. Growth, livability, and feed conversion of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poult. Sci.  82: 1500– 1508. Google Scholar CrossRef Search ADS PubMed  Havenstein G. B., Ferket P. R., Qureshi M. A.. 2003. Carcass composition and yield of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poult. Sci.  82: 1509– 1518. Google Scholar CrossRef Search ADS PubMed  Joseph N. S., Robinson F. E., Korver D. R., Renema R. A.. 2000. Effect of dietary protein intake during the pullet-to-breeder transition period on early egg weight and production in broiler breeders. Poult. Sci.  79: 1790– 1796. Google Scholar CrossRef Search ADS PubMed  Joseph N. S., Dulaney A. A. J., Robinson F. E., Renema R. A., Zuidhof M. J.. 2002. The effects of age at photostimulation and dietary protein intake on reproductive efficiency in three strains of broiler breeders varying in breast yield. Poult. Sci.  81: 597– 607. Google Scholar CrossRef Search ADS PubMed  Keshavarz K., Nakajima S.. 1995. The effect of dietary manipulations of energy, protein, and fat during the growing and laying periods on early egg weight and egg components. Poult. Sci.  74: 50– 61. Google Scholar CrossRef Search ADS PubMed  Laughlin K. F. 2009. ‘ Breeder management: How did we get here?’. Pages 10– 25 in: Biology of Breeding Poultry . Poult. Sci. Series Vol. 29. Hocking P. M. ed. CABI. Wallingford, UK. Google Scholar CrossRef Search ADS   Lewis P. D. 2006. A review of lighting for broiler breeders. Br. Poult. Sci.  47: 393– 404. Google Scholar CrossRef Search ADS PubMed  Lilburn M. S., Myers-Miller D. J.. 1990. Effect of body weight, feed allowance, and dietary protein intake during the prebreeder period on early reproductive performance of broiler breeder hens. Poult. Sci.  69: 1118– 1125. Google Scholar CrossRef Search ADS PubMed  Lopez G., Leeson S.. 1995. Response of broiler breeders to low-protein diets: 1. Adult breeder performance. Poult. Sci.  74: 685– 695. Google Scholar CrossRef Search ADS PubMed  Lopez G., Leeson S.. 1995. Nitrogen content of manure from older broiler breeders fed varying quantities of crude protein. J. Appl. Poult. Res.  4: 390– 394. Google Scholar CrossRef Search ADS   Lopez G., Leeson S.. 1995. Response of broiler breeders to low-protein diets: 2. Offspring performance. Poult. Sci.  74: 696– 701. Google Scholar CrossRef Search ADS PubMed  Mejia L., McDaniel C. D., Corzo A.. 2012. Dietary influence of digestible lysine concentration on Cobb 500 hen broiler breeder reproductive performance. Poult. Sci.  91: 426– 431. Google Scholar CrossRef Search ADS PubMed  Mejia L., McDaniel C. D., Kidd M. T., Lopez K., Corzo A.. 2013. Evaluation of carryover effects of dietary lysine intake by Cobb 500 broiler breeder hens. Poult. Sci.  92: 709– 718. Google Scholar CrossRef Search ADS PubMed  Mohiti-Asli M., Shivazad M., Zaghari M., Rezaian M., Aminzadeh S., Mateos G. G.. 2012. Effects of feeding regimen, fiber inclusion, and crude protein content of the diet on performance and egg quality and hatchability of eggs of broiler breeder hens. Poult. Sci.  91: 3097– 3106. Google Scholar CrossRef Search ADS PubMed  Pearson R. A., Herron K. M.. 1981. Effects of energy and protein allowances during lay on the reproductive performance of broiler breeder hens. Br. Poult. Sci. Sci . 22: 227– 239. Google Scholar CrossRef Search ADS   Pearson R. A., Herron K. M.. 1982. Effects of maternal energy and protein intakes on the incidence of malformations and malpositions of the embryo and time of death during incubation. Br. Poult. Sci.  23: 71– 77. Google Scholar CrossRef Search ADS PubMed  Pishnamazi A., Renema R. A., Zuidhof M. J., Robinson F. E.. 2014. Effect of age at photostimulation on sexual maturation in broiler breeder pullets. Poult. Sci . 93: 1274– 1281. Google Scholar CrossRef Search ADS PubMed  Renema R. A., Robinson F. E., Goerzen P. R., Zuidhof M. J.. 2001. Effects of altering growth curve and age at photostimulation in female broiler breeders. 2. Egg production parameters. Can. J. Anim. Sci. Sci . 81: 477– 486. Google Scholar CrossRef Search ADS   Renema R. A., Robinson F. E., Goerzen P. R.. 2001. Effects of altering growth curve and age at photostimulation in female broiler breeders. 1. Reproductive development. Can. J. Anim. Sci.  81: 467– 476. Google Scholar CrossRef Search ADS   Renema R. A., Rustad M. E., Robinson F. E.. 2007. Implications of changes to commercial broiler and broiler breeder body weight targets over the past 30 years. World's Poult. Sci. J.  63: 457– 472. Google Scholar CrossRef Search ADS   Renema R. A., Moraes T. G. V., Zuidhof M. J.. 2013. Effects of broiler breeder nutrition on chick quality and broiler growth. Pages 212– 222 in Proc. 2nd Int. Poult. Meat Congress , Antalya, Turkey. Robinson F. E., Wautier T. A., Hardin R. T., Robinson N. A., Wilson J. L., Newcombe M., McKay R. I.. 1996. Effects of age at photostimulation on reproductive efficiency and carcass characteristics. 1. Broiler breeder hens. Can. J. Anim. Sci.  76: 275– 282. Google Scholar CrossRef Search ADS   Robinson F. E., Zuidhof M. J., Renema R. A.. 2007. Reproductive efficiency and metabolism of female broiler breeders as affected by genotype, feed allocation, and age at photostimulation. 1. Pullet growth and development. Poult. Sci.  86: 2256– 2266. Google Scholar CrossRef Search ADS PubMed  Spratt R. S., Leeson S.. 1987. Broiler breeder performance in response to diet protein and energy. Poult. Sci.  66: 683– 693. Google Scholar CrossRef Search ADS PubMed  Tona K., Onagbesan O., De Ketelaere B., Decuypere E., Bruggeman V.. 2004. Effects of Age of Broiler Breeders and Egg Storage on Egg Quality, Hatchability, Chick Quality, Chick Weight, and Chick Posthatch Growth to Forty-Two Days. J. Appl. Poult. Res.  13: 10– 18. Google Scholar CrossRef Search ADS   Van Emous R. A., Kwakkel R. P., van Krimpen M. M., van den Brand H., Hendriks W. H.. 2015a. Effects of growth patterns and dietary protein levels during rearing of broiler breeders on fertility, hatchability, embryonic mortality and offspring performance. Poult. Sci.  94: 681– 691. Google Scholar CrossRef Search ADS   Van Emous R. A. 2015. Body composition and reproduction in broiler breeders: impact of feeding strategies . PhD Diss. Wageningen University, Wageningen, the Netherlands. Van Emous R. A., Kwakkel R. P., van Krimpen M. M., Hendriks W. H.. 2015b. Effects of dietary protein levels during rearing and dietary energy levels during lay on body composition and reproduction in broiler breeder females. Poult. Sci.  94: 1030– 1042. Google Scholar CrossRef Search ADS   Whitehead C. C., Pearson R. A., Herron K. M., 1985. Biotin requirements of broiler breeders fed diets of different protein content and effect of insufficient biotin on the viability of progeny. Br. Poult. Sci.  26: 73– 82. Google Scholar CrossRef Search ADS PubMed  Yuan T., Lien R. J., McDaniel G. R.. 1994. Effects of increased rearing period body weights and early photostimulation on broiler breeder egg production. Poult. Sci.  73: 792– 800. Google Scholar CrossRef Search ADS PubMed  Zuidhof M. J., Schneider B. L., Carney V. L., Korver D. R., Robinson F. E.. 2014. Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005. Poult. Sci.  93: 2970– 2982. Google Scholar CrossRef Search ADS PubMed  © 2018 Poultry Science Association Inc. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

Poultry ScienceOxford University Press

Published: Mar 5, 2018

There are no references for this article.

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create lists to
organize your research

Export lists, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off