# Effects of production systems on the carcass and meat quality characteristics of spent laying hens

Effects of production systems on the carcass and meat quality characteristics of spent laying hens ABSTRACT This study evaluated the carcass characteristics and meat quality attributes of spent laying hens raised under conventional battery cage and free-range systems. Thirty free-range and 30 conventional battery-caged Lohmann Brown-Elite spent laying hens of 53 and 40 wk of age, respectively were obtained from a commercial egg producer. Carcass, portion, and organ weights and percentages were determined. Physicochemical analyses were performed on thigh and breast meat samples. Caged hens had heavier (P ≤ 0.05) warm and cold carcasses, thighs, wings, and feet. The percentages of the breast (26.1 ± 0.51 vs. 28.3 ± 0.28), drum, breast bones, breast thaw and cooking loss, and thigh cooking loss were higher (P ≤ 0.05) for free-range than for caged hens. Free-range hens had heavy (P ≤ 0.05) gizzards (33.9 ± 1.04 vs. 30.5 ± 0.73) and bones and a lower (P ≤ 0.05) breast meat percentage (47.3 ± 0.94 vs. 51.7 ± 1.35). Meat redness (a*) (0.54 ± 0.222 vs. 1.40 ± 0.135) and hue angle, skin redness (a*), breast (12.37 ± 0.411 vs. 17.10 ± 0.751), and thigh (29.68 ± 0.306 vs. 39.75 ± 0.826) Warner-Bratzler shear force values (N), breast moisture, and thigh ash content were higher (P ≤ 0.05) for free-range hens. Caged hens had a higher (P ≤ 0.05) thigh thaw loss percentage and breast ash content. Production system significantly influenced the carcass characteristics and meat quality of spent laying hens. The results of this study supply baseline information for the utilization of spent laying hens by the poultry industry and consumers. INTRODUCTION The nutrition, freedom from diseases, behavioral expression, and ability to adapt to environmental stress of laying hens is defined by the production system, which impacts hens’ welfare and egg productivity. Modern laying hen strains are offspring of wild fowl. Although genetic breeding is aimed at eradicating some of the traits (broodiness, search for food, and social interaction) of wild fowl from laying hens (Price, 2002), the modern laying hen strains still preserve a number of ancestral behaviors (e.g., building nests, foraging, and night perching) (Kjaer and Mench, 2003; Bingham, 2013). The conventional battery cage system (caged) has been criticized (Mugnai et al., 2011) and banned in some countries (most of Europe) for restraining laying hens from exposing their natural behavioral patterns (EC, 1999). To date, consumers are well informed about the issue of animal welfare and how it relates to final products (Napolitano et al., 2010). Rodić et al. (2010) and Napolitano et al. (2010) highlighted that consumers are willing to pay 20% more for eggs produced under free-range than caged systems. Also, foraging on pasture imparts specific quality characteristics such as n3 fatty acids into the meat and eggs; hence, many consumers perceive free-range eggs and meat as a functional food (Sossidou et al., 2015; Perić et al., 2016). For slow-growing broilers, several studies have reported significant differences in body weight, meat and skin color, abdominal and meat fat content, and tenderness between free-range and floor reared birds (Wang et al., 2009; Funaro et al., 2014). Free-range systems impart desired meat traits such as yellowness of the skin and meat, chewiness, vitamins, low fat content, a high content of polyunsaturated fatty acids (PUFA) and a low n6: n3 PUFA ratio (Castellini et al., 2002; Michalczuk et al., 2014; 2017). However, not all results are in agreement with these authors, e.g., Funaro et al. (2014) found a higher n6: n-3 ratio in birds reared in a free-range system. The influence of a free-range production system on meat quality has been extensively researched for broiler chickens, turkeys, and ducks. However, for laying hens, studies on the influence of production system are limited to table eggs. There is little or no literature on carcass and meat quality characteristics of free-range and cage reared spent laying hens. Therefore, the aim of this study was to evaluate the carcass characteristics and meat quality attributes of spent laying hens (Lohmann Brown-Elite) raised under conventional battery cage and free-range systems. MATERIALS AND METHODS Experimental Design A total of 60 Lohmann Brown-Elite spent laying hens was obtained from a commercial egg producer (ethical clearance number MUC441SSEM01). From a large commercial flock reared in battery cages (caged), a group of 30 hens was selected; one hen was randomly selected per cage (each cage contained 10 hens). Thirty free-range raised hens also were also randomly selected. All hens were fed the same commercial layer diet. Caged hens were 40 wk of age while free-range hens were 53 wk of age. Age after sexual maturity (18 wk of age) has little effect on muscle structural and chemical changes (Barbut, 2015), so differences in age were not considered to be important in this study. Slaughtering All hens were transported in certified chicken crates from the farm to a certified commercial poultry abattoir. The hens were held for 12 h in a free-range facility and provided with feed and water ad libitum before being transported to the abattoir for slaughter: Electrical stunning with 50 to 70 V for 3 to 5 s, immediately followed by exsanguination through severing of the carotid arteries and jugular veins. After bleeding for 5 min, the carcasses were submerged in a water bath at 60°C for 2 min, mechanically defeathered in a rotating drum for 30 s, and washed. Carcass Yield, Portioning, and Deboning The weights of the warm and cold (after 24 h chilling) carcasses (with neck skin), 8 intact portions, gizzard, liver, heart, feet, and head were recorded using a sensitive weighing scale (Carcass: DIGI, Model: DS-673; Tokyo, Japan. Organs: RADWAG, Model: PS 750/C/2, Warsaw, Poland) 30 min post mortem. After chilling at 4°C (±1°C) for 24 h, the carcasses were portioned into 8 pieces: breasts, thighs, drums and wings (NAMP, 2007; DAFF, 2012). All breast portions were deboned after physical analyses (pH and color): skin (with fat); bones and meat were weighed individually. The right breast muscles (M. Pectoralis major and M. Pectoralis minor) and right thigh (bone in and skin on) were individually vacuum packed and stored (6 wk) at –20°C for further analyses. The left breast meat (M. Pectoralis major and M. Pectoralis minor) and left thigh meat (deboned, skin on) were individually vacuum packed and stored (24 h) at 4°C (±1°C) for proximate analysis. The portions and organs were presented as average weights as well as percentages of the cold carcass weights. The breast meat, bones, and skin were presented as individual weights and as a percentage of the intact breast portion weight. Physical Measurements The pH and color readings were measured after 24 h of chilling at 4°C (±1°C). The pH was measured using a calibrated handheld portable pH meter (CRISON pH 25+, CRISON instruments, Madrid, Spain) before portioning. A spectro-guide 45/0 gloss colorimeter (Cat no: 6801; BYK-Gardner GmbH, Hamburg, Germany) was standardized against a white calibration tile (D65/10°: L* = 95.73; a* = −0.83; b* = 1.31) and used to measure skin and meat color according to CIE (1976). Skin color was measured on both breasts (before portioning), and meat color was measured on the right deboned breast meat. The hue angle (hab) (°) and chroma values (C*) were calculated using the a* and b* values (AMSA, 2012): \begin{equation*}{h_{ab}} = ta{n^{ - 1}}\left\{ {\frac{{{b^*}}}{{{a^*}}}} \right\}\quad C^{*} = \sqrt {{{({a^*})}^2} + {{({b^*})}^2}} \end{equation*} Thaw and cooking meat losses were measured on the right breast muscle (M. Pectoralis major and M. Pectoralis minor) and thigh (bone in and skin on) according to Honikel (1998) and AMSA (2015). The breasts and thighs reached an internal temperature of 80°C within 7 min and 35 min of cooking, respectively. All cooking times, endpoint temperatures, and cooling times were determined in a pre-trial to suit the meat samples in the study. The Warner-Bratzler shear force (WBSF) test was used to measure the instrumental shear force (N) of the cooked meat samples (Lyon and Lyon, 1997). For the thighs, the M. Iliotibialis and M. Biceps femoris were excised, and 2 adjacent strips of 1 cm width x 1 cm breadth x 4 cm length (parallel to the muscle fiber) were sampled, with both muscles sheared at the same time. An Instron Universal Testing Machine (Instron UTM, Model 2519–107) attached to a Warner-Bratzler fitting was used to determine the force required to shear the cooked rectangular (1 × 1 cm) meat strips perpendicular to the muscle fiber direction. The Warner-Bratzler fitting was a 1 mm thick triangular (V-notch) blade with a semi-circular cutting edge (radius of 0.508 mm). The Instron was driven with a 2 kN compression load cell recording in Newton (N). The shear test was executed at a speed of 200 mm/min. Chemical Analysis Chemical analyses were performed on deboned breast meat (M. Pectoralis major and M. Pectoralis minor) and thigh (skin on) samples. The breast and thigh meat (skin on) samples were chilled at 4°C (±1°C) for 24 h after deboning, homogenized (DAMPA CT-35 N Bowl cutter, Golasecca (VA) Italy) for 20 s, vacuum packed, and stored at –20°C until chemical analyses were executed. Prior to each analysis, meat samples were defrosted at 4°C (±1°C) for 12 hours. The moisture and ash content (%) of the meat samples was determined by using a 2.5 g homogenized meat sample according to the Official Methods of Analysis 934.01 and 942.01, respectively (AOAC, 2002a; 2002b). A 5 g homogenized meat sample was used for the chloroform/methanol (1:2 v/v for breasts; 2:1 v/v for thighs) extraction technique as described by Lee et al. (1996) to determine the total lipid content (%). The defatted dried meat sample was used to determine the total crude protein content (%) according to the Dumas combustion method 992.15 (AOAC, 2002c) and protocol stipulated by Geldenhuys et al. (2013). Statistical Analysis All data collected in the study were subjected to the General Linear Model (GLM) procedure of SAS (SAS, 2003), and a univariate analysis of variance (ANOVA) was generated. A Shapiro-Wilk test was executed for a non-normality of residuals test (Shapiro and Wilk, 1965). Outliers were identified and removed from the data when non-normality was significant (P ≤ 0.05). Differences between treatment means were tested according to Fisher's least significant difference (LSD) test of SAS. Means with a standard error (SE) of the mean were used to present the data. A significant level of P ≤ 0.05 was used to conclude differences between means. For all the variables measured in duplicate or more, means were calculated and used in statistical analysis. RESULTS Carcass Characteristics Table 1 shows carcass characteristics of spent laying hens from different production systems. Caged hens had heavier warm and cold carcass (P ≤ 0.05), thigh and wing weights (P ≤ 0.05) and increased percentage thigh (P < 0.001) compared with free-range hens. The breast and drum percentages were higher (P ≤ 0.05) for free-range than caged hens. The gizzard weight and percentage were higher (P ≤ 0.05) for the free-range than caged hens. The non-carcass components, neck, and head, did not differ (P > 0.05) between production systems, while caged hens had heavier (P ≤ 0.001) feet. Free-range hens had heavier (P < 0.001) breast bone weights, higher (P < 0.001) bone percentages, and lower (P ≤ 0.05) meat percentages (Table 1). Table 1. Means (± SE) of carcass characteristics of caged and free-range spent laying hens. Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 1Means with n = 30 per treatment. 2Means with n = 15 per treatment. 3Calculated as a percentage of the cold carcass weight. 4Calculated as a percentage of the warm carcass weight. 5Calculated as a percentage of the right breast portion. View Large Table 1. Means (± SE) of carcass characteristics of caged and free-range spent laying hens. Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 1Means with n = 30 per treatment. 2Means with n = 15 per treatment. 3Calculated as a percentage of the cold carcass weight. 4Calculated as a percentage of the warm carcass weight. 5Calculated as a percentage of the right breast portion. View Large Physical Characteristics The effects of production systems on the physical attributes of spent laying hen meat are shown in Table 2. Free-range hens had higher (P ≤ 0.05) breast thaw and cooking loss percentages, thigh cooking loss percentages, meat redness (a*), hue angle value, skin redness (a*), and breast and thigh shear force values. Caged hens had higher (P < 0.001) thigh thaw loss percentages. Table 2. Means (± SE) of physical attributes of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 1Means with n = 12 replicates per treatment. 2Means with n = 30 replicates per treatment. View Large Table 2. Means (± SE) of physical attributes of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 1Means with n = 12 replicates per treatment. 2Means with n = 30 replicates per treatment. View Large Chemical Composition The proximate composition of the breast (skinless) and thigh (skin on) meat of caged and free-range spent laying hens is shown in Table 3. Free-range hens showed higher (P ≤ 0.05) breast meat moisture content and lower thigh meat ash content. However, the breast ash content of the caged hens was higher (P < 0.001). Crude protein and fat of the breast and thigh meat, as well as thigh meat moisture content, did not differ (P > 0.05) between caged and free-range hens. Table 3. Means1 (± SE) of proximate composition of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 1Means with n = 12 per treatment. View Large Table 3. Means1 (± SE) of proximate composition of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 1Means with n = 12 per treatment. View Large DISCUSSION Carcass Characteristics The lower carcass and portion yields for free-range spent laying hens in the present study could be ascribed to a number of factors: environmental temperatures, light intensity, diet, exercise, and pasture. All the above-mentioned factors could have interfered with growth performance of the laying hens, and hence carcass and portion yields. Moreover, the increase in the digestive tract weight of the free-range birds to adapt to high fiber in natural pastures could also negatively impact carcass weight and composition (Ponte et al., 2008; Mateos et al., 2012). To qualify as a free-range production system in South Africa, 50% of the accessible outdoor area must be covered with green grass (SAPA, 2012). The variation in the percentage yield of the portions could be attributed to the differences in the portion weights. For instance, the caged hens had heavier thighs than free-range hens, which would have led to the higher thigh and lower breast percentage. Free-range systems favor breast muscle development due to the motory behavior of the birds (Castellini et al., 2002). Access to pasture in the free-range system could be the reason for the increased gizzard weight and percentage for the free-range hens; it was noted that the hens had access to pastures that had some vegetative growth. However, it was not determined whether they had consumed some of this plant material. High dietary fiber diets stimulate gizzard muscle development in order to grind and digest feed effectively (Mateos et al., 2012). The heavier feet for caged hens could be a result of high fat and less connective tissue in the caged hen's feet. Free-range bird feet go through intensive movement and exercise, which could increase the amount of connective tissue and lower the fat and muscle content. Additionally, caged birds are prone to foot lesions due to high stocking density and the nature of the cage floors (Farhadi and Hosseini, 2016; Kiyma et al., 2016). Foot lesions could have contributed to the heavy feet of the caged hens, as they do cause foot swelling. The heavy breast bones for free-range hens could be attributed to the development of bone and cartilage of the breast in order to support muscles for the intense wing movement (Lewis et al., 1997). Although free-range hens are not flight birds, most of the times they do attempt to fly for a short distance. For instance, hens under free-range systems fly from litter to perches as avoidance behavior and to escape capture. Physical Characteristics The high thigh thaw loss of caged hens could be ascribed to the numerically high intramuscular fat content of the caged hen thighs coupled with the state of the protein. Moreover, caged hen thighs in the study had a high level of abdominal fat attached. Although water-holding capacity is more related to meat protein functional properties and pH (Bowker and Zhuang, 2015), Colmenero (2014) noted that thaw and cooling losses, which are a function of the water-holding capacity of meat, also can be influenced by meat fat content when stored and cooked. The fluctuation of environmental temperatures coupled with high average temperatures, reduces the water-holding capacity of muscles (Wang et al., 2009). Free-range hens are exposed to uncontrolled environments (as discussed previously). The aforementioned aspects could be the cause of the high thaw and cooking losses of the free-range hen meat. Castellini et al. (2002) also reported an increase in the cooking loss of the breast (indoor: 31.1 and 30.3%; free-range: 34.0 and 33.5%) and thigh (indoor: 32.7 and 31.0%; free-range: 35.2 and 34.0%) when broiler chickens were given access to free-range at 51 and 81 d of age, respectively. The cooking loss results in this study are similar to those observed by Castellini et al. (2002). However, these findings contradict those of Funaro et al. (2014). Thaw and cooking loss results in this study also pose a challenge to literature on the relationship between muscle physical as well as chemical properties and water-holding capacity. Fu et al. (2014) noted that free-range birds had larger muscle fiber diameter. A positive association exists between muscle fiber diameter and plasma creatine kinase activity, which may be revealed in protein turnover and hence in muscle growth (Funaro et al., 2014). Furthermore, free-range hens are bound to have higher collagen thickness and cross-linking owing to their higher level of motory activity (Astruc, 2014). The latter factors are expected to result in a higher water-holding capacity, hence, low thaw and cooking losses; however, this is not the case in this study, as higher thaw and cooking loss percentages were recorded for free-range hens than for caged hens (Table 2). The high thaw and cooking loss observed in the current study is detrimental to meat quality, as it may result in drier and tougher meat. The effect of production systems was not observed in the meat pH. The pH values (6.15 to 6.32) in this study were higher than the 5.8 expected, which could be attributed to the light weight of the birds and pre-slaughter handling. Michalczuk et al. (2017) explained that light birds are highly predisposed to pre-slaughter stress as they tend to struggle a lot along the slaughter lines antemortem, since they are accustomed to being active. The prolonged struggling depletes the glycogen reserves resulting in higher ultimate pH values of the meat (Honikel, 2014). Moreover, these birds were transported the previous afternoon and held overnight in a free-range holding facility (with ad lib access to water and feed, although the feed was different from what they had been fed during their production life) prior to being transported to the abattoir. If the birds had not consumed any feed during this period, their muscle glycogen reserves may have become depleted, and this would have resulted in a higher muscle pH postmortem. Nonetheless, the pH values recorded are in acceptable ranges as observed in other studies (Funaro et al., 2014; Michalczuk et al., 2017). Skin and meat color are key determinants of consumers’ acceptance of chicken meat (Barbut, 2015). According to CIE (1976), redness (a*) spans from +60 (red) to -60 (green). The use of redness (a*) to measure chicken meat color is limited, as myoglobin (the protein that determines redness of meat) is not readily detectable in chicken meat (Zhuang and Savage, 2012; Barbut, 2015). The increase in the redness (a*) of the skin of free-range compared to caged birds (Table 2) indicates undesirable pink and red tones (Ponte et al., 2008). Although most of the literature agrees that pasture imparts a desirable yellow characteristic to the skin (Fanatico et al., 2007; Michalczuk et al., 2017), Barbut (2015) noted that submerging in warm water (as in this study) results in a loss of this desirable, traditional yellowness and may even lead to the skin becoming more red. Thus, the influence of scalding could have resulted in the skin color differences between caged and free-range hens in this study. The higher redness of the muscle from the free-range hens could be ascribed to the increased motor activity, as noted by Castellini et al. (2002). The redness values of the current study show a similar trend to that as reported for the skin by Fanatico et al. (2007) (caged: -0.17; free-range: 0.44; for slow-growth genotype) and for meat by Skŕivan et al. (2015) (caged: 0.3; free-range: 1.9). Aalhus et al. (2009) noted that a strong relationship exists between muscle fiber diameter and meat tenderness with meat containing small muscle fiber diameters being more tender. Free-range systems have been reported to increase muscle development, which translates into larger fiber diameters (Fu et al., 2014; Funaro et al., 2014). Although muscle fiber diameter was not analyzed in the current study, an increase in muscle fiber diameter could be the reason for the higher shear force values recorded for both the breast and thigh meat of free-range hens. Furthermore, the motor activity of free-range birds is known to increase the amount of connective tissue and collagen cross-linkages (Astruc, 2014), which could lead to higher shear force values. Castellini et al. (2002) (breast: 20.59 N vs. 26.58 N; thigh: 28.15 N vs. 34.13 N at 81 d of age) results also showed significant higher shear force values for broiler chickens reared under free-range than indoor systems as in this study. However, there are studies in which no significant differences in shear force values of meat were recorded between free-range and caged chickens (Fanatico et al., 2005b; Wang et al., 2009). The breast shear force values (caged: 12.37 N and free-range: 17.10 N) in the current study are within range with those of broiler chickens recorded by Chen et al. (2007) (11.9 N to 17.36 N) and Hashim et al. (2013) (16.96 N to 18.63 N). Chuaynukool et al. (2007) reported spent laying hen breast meat as being tougher (30.79 N) than indigenous (22.36 N) and broiler (15.59 N) meat. The lower than expected shear force values of spent laying hen breast meat in this study could be characteristic of the lower breast weights compared to those of broiler chickens, as Lyon et al. (2010) concluded that breast weight is correlated to tenderness, with lower weights being more tender. Chemical Composition The nutrient composition (moisture, protein, fat, and ash) of spent laying hen meat recorded (Table 3) in this study are in range with those of chicken in literature by Funaro et al. (2014) (breast: moisture 73.4%; protein 23.3%; fat 1.0%; ash 1.2%; and thigh [skin on]: moisture 67.9%; protein 18.6%; fat 10.8%; and ash 1.0%) and Keeton et al. (2014) (meat: moisture 75.5%; protein 21.4%; fat 3.1%; and ash 1.0%). However, the breast meat moisture content results in the current study contradict those of Fanatico et al. (2005b) and Funaro et al. (2014). These authors found indoor broiler chicken breast meat to have higher moisture content (72.2 and 73.4%) than free-range reared broilers (71.1 and 72.5%). Keeton et al. (2014) noted that the relationship among moisture, protein, and ash is inversely proportional to the fat content of the meat. The literature generally agrees that free-range production decreases the intramuscular fat content of meat (Fu et al., 2014; Funaro et al., 2014). The reduction in intramuscular fat of the breast and thigh also was noted in the current study, although it was not significant. Based on Keeton et al. (2014), the low fat content of the breast meat of free-range hens could have resulted in the higher moisture content observed in this study. Nonetheless, other studies have reported no significant differences among the moisture, protein, fat, or ash content for free-range and caged birds (Michalczuk et al., 2014; Skŕivan et al., 2015; 2017). CONCLUSIONS Production systems had an effect on carcass characteristics and physical and chemical attributes of the meat derived from spent laying hens. The carcass and portion weights of the spent laying hens were also lower than the minimal market weights (carcass weight: 1.5 kg) of broiler chickens. This constitutes a further reason for the lower economic value of spent laying hens. The free-range production system increased the weight of the prime economic portion (breast); however, the meat percentage of the breast portion was reduced. As expected, the selected physical attributes of free-range hen meat were higher than those of caged hens, which could be attributed to increased motor activities and the uncontrolled environmental conditions experienced by the former. The skinless breast meat fat content of spent laying hens in this study was lower than that of broiler chicken breasts reported in the literature. Thus, we might recommend spent laying hen breast meat to consumers concerned about high fat content in chicken. Further studies are recommended to evaluate the fatty acids and sensory profile of the meat of spent laying hens as influenced by production systems. ACKNOWLEDGMENTS This research is supported by the South African Research Chairs Initiative (SARChI) and funded by the South African Department of Science and Technology (UID: 84633), as administered by the National Research Foundation (NRF) of South Africa. The financial assistance of the NRF towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at are those of the authors and are not necessarily to be attributed to the NRF. We also acknowledge Nulaid Company, which donated the spent laying hens. REFERENCES Aalhus J. L. , Robertson W. M. , Jin Y. . 2009 . Muscle fiber characteristics and their relation to meat quality . Pages 97 – 114 in Applied Muscle Biology and Meat Science . Du M , McCormick R. J. ed. CRC press , New York, USA . Google Scholar CrossRef Search ADS AMSA . 2012 . Meat Color Measurement Guidelines . AMSA , Illinois, USA . AMSA . 2015 . 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# Effects of production systems on the carcass and meat quality characteristics of spent laying hens

, Volume Advance Article (6) – Mar 22, 2018
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### Abstract

ABSTRACT This study evaluated the carcass characteristics and meat quality attributes of spent laying hens raised under conventional battery cage and free-range systems. Thirty free-range and 30 conventional battery-caged Lohmann Brown-Elite spent laying hens of 53 and 40 wk of age, respectively were obtained from a commercial egg producer. Carcass, portion, and organ weights and percentages were determined. Physicochemical analyses were performed on thigh and breast meat samples. Caged hens had heavier (P ≤ 0.05) warm and cold carcasses, thighs, wings, and feet. The percentages of the breast (26.1 ± 0.51 vs. 28.3 ± 0.28), drum, breast bones, breast thaw and cooking loss, and thigh cooking loss were higher (P ≤ 0.05) for free-range than for caged hens. Free-range hens had heavy (P ≤ 0.05) gizzards (33.9 ± 1.04 vs. 30.5 ± 0.73) and bones and a lower (P ≤ 0.05) breast meat percentage (47.3 ± 0.94 vs. 51.7 ± 1.35). Meat redness (a*) (0.54 ± 0.222 vs. 1.40 ± 0.135) and hue angle, skin redness (a*), breast (12.37 ± 0.411 vs. 17.10 ± 0.751), and thigh (29.68 ± 0.306 vs. 39.75 ± 0.826) Warner-Bratzler shear force values (N), breast moisture, and thigh ash content were higher (P ≤ 0.05) for free-range hens. Caged hens had a higher (P ≤ 0.05) thigh thaw loss percentage and breast ash content. Production system significantly influenced the carcass characteristics and meat quality of spent laying hens. The results of this study supply baseline information for the utilization of spent laying hens by the poultry industry and consumers. INTRODUCTION The nutrition, freedom from diseases, behavioral expression, and ability to adapt to environmental stress of laying hens is defined by the production system, which impacts hens’ welfare and egg productivity. Modern laying hen strains are offspring of wild fowl. Although genetic breeding is aimed at eradicating some of the traits (broodiness, search for food, and social interaction) of wild fowl from laying hens (Price, 2002), the modern laying hen strains still preserve a number of ancestral behaviors (e.g., building nests, foraging, and night perching) (Kjaer and Mench, 2003; Bingham, 2013). The conventional battery cage system (caged) has been criticized (Mugnai et al., 2011) and banned in some countries (most of Europe) for restraining laying hens from exposing their natural behavioral patterns (EC, 1999). To date, consumers are well informed about the issue of animal welfare and how it relates to final products (Napolitano et al., 2010). Rodić et al. (2010) and Napolitano et al. (2010) highlighted that consumers are willing to pay 20% more for eggs produced under free-range than caged systems. Also, foraging on pasture imparts specific quality characteristics such as n3 fatty acids into the meat and eggs; hence, many consumers perceive free-range eggs and meat as a functional food (Sossidou et al., 2015; Perić et al., 2016). For slow-growing broilers, several studies have reported significant differences in body weight, meat and skin color, abdominal and meat fat content, and tenderness between free-range and floor reared birds (Wang et al., 2009; Funaro et al., 2014). Free-range systems impart desired meat traits such as yellowness of the skin and meat, chewiness, vitamins, low fat content, a high content of polyunsaturated fatty acids (PUFA) and a low n6: n3 PUFA ratio (Castellini et al., 2002; Michalczuk et al., 2014; 2017). However, not all results are in agreement with these authors, e.g., Funaro et al. (2014) found a higher n6: n-3 ratio in birds reared in a free-range system. The influence of a free-range production system on meat quality has been extensively researched for broiler chickens, turkeys, and ducks. However, for laying hens, studies on the influence of production system are limited to table eggs. There is little or no literature on carcass and meat quality characteristics of free-range and cage reared spent laying hens. Therefore, the aim of this study was to evaluate the carcass characteristics and meat quality attributes of spent laying hens (Lohmann Brown-Elite) raised under conventional battery cage and free-range systems. MATERIALS AND METHODS Experimental Design A total of 60 Lohmann Brown-Elite spent laying hens was obtained from a commercial egg producer (ethical clearance number MUC441SSEM01). From a large commercial flock reared in battery cages (caged), a group of 30 hens was selected; one hen was randomly selected per cage (each cage contained 10 hens). Thirty free-range raised hens also were also randomly selected. All hens were fed the same commercial layer diet. Caged hens were 40 wk of age while free-range hens were 53 wk of age. Age after sexual maturity (18 wk of age) has little effect on muscle structural and chemical changes (Barbut, 2015), so differences in age were not considered to be important in this study. Slaughtering All hens were transported in certified chicken crates from the farm to a certified commercial poultry abattoir. The hens were held for 12 h in a free-range facility and provided with feed and water ad libitum before being transported to the abattoir for slaughter: Electrical stunning with 50 to 70 V for 3 to 5 s, immediately followed by exsanguination through severing of the carotid arteries and jugular veins. After bleeding for 5 min, the carcasses were submerged in a water bath at 60°C for 2 min, mechanically defeathered in a rotating drum for 30 s, and washed. Carcass Yield, Portioning, and Deboning The weights of the warm and cold (after 24 h chilling) carcasses (with neck skin), 8 intact portions, gizzard, liver, heart, feet, and head were recorded using a sensitive weighing scale (Carcass: DIGI, Model: DS-673; Tokyo, Japan. Organs: RADWAG, Model: PS 750/C/2, Warsaw, Poland) 30 min post mortem. After chilling at 4°C (±1°C) for 24 h, the carcasses were portioned into 8 pieces: breasts, thighs, drums and wings (NAMP, 2007; DAFF, 2012). All breast portions were deboned after physical analyses (pH and color): skin (with fat); bones and meat were weighed individually. The right breast muscles (M. Pectoralis major and M. Pectoralis minor) and right thigh (bone in and skin on) were individually vacuum packed and stored (6 wk) at –20°C for further analyses. The left breast meat (M. Pectoralis major and M. Pectoralis minor) and left thigh meat (deboned, skin on) were individually vacuum packed and stored (24 h) at 4°C (±1°C) for proximate analysis. The portions and organs were presented as average weights as well as percentages of the cold carcass weights. The breast meat, bones, and skin were presented as individual weights and as a percentage of the intact breast portion weight. Physical Measurements The pH and color readings were measured after 24 h of chilling at 4°C (±1°C). The pH was measured using a calibrated handheld portable pH meter (CRISON pH 25+, CRISON instruments, Madrid, Spain) before portioning. A spectro-guide 45/0 gloss colorimeter (Cat no: 6801; BYK-Gardner GmbH, Hamburg, Germany) was standardized against a white calibration tile (D65/10°: L* = 95.73; a* = −0.83; b* = 1.31) and used to measure skin and meat color according to CIE (1976). Skin color was measured on both breasts (before portioning), and meat color was measured on the right deboned breast meat. The hue angle (hab) (°) and chroma values (C*) were calculated using the a* and b* values (AMSA, 2012): \begin{equation*}{h_{ab}} = ta{n^{ - 1}}\left\{ {\frac{{{b^*}}}{{{a^*}}}} \right\}\quad C^{*} = \sqrt {{{({a^*})}^2} + {{({b^*})}^2}} \end{equation*} Thaw and cooking meat losses were measured on the right breast muscle (M. Pectoralis major and M. Pectoralis minor) and thigh (bone in and skin on) according to Honikel (1998) and AMSA (2015). The breasts and thighs reached an internal temperature of 80°C within 7 min and 35 min of cooking, respectively. All cooking times, endpoint temperatures, and cooling times were determined in a pre-trial to suit the meat samples in the study. The Warner-Bratzler shear force (WBSF) test was used to measure the instrumental shear force (N) of the cooked meat samples (Lyon and Lyon, 1997). For the thighs, the M. Iliotibialis and M. Biceps femoris were excised, and 2 adjacent strips of 1 cm width x 1 cm breadth x 4 cm length (parallel to the muscle fiber) were sampled, with both muscles sheared at the same time. An Instron Universal Testing Machine (Instron UTM, Model 2519–107) attached to a Warner-Bratzler fitting was used to determine the force required to shear the cooked rectangular (1 × 1 cm) meat strips perpendicular to the muscle fiber direction. The Warner-Bratzler fitting was a 1 mm thick triangular (V-notch) blade with a semi-circular cutting edge (radius of 0.508 mm). The Instron was driven with a 2 kN compression load cell recording in Newton (N). The shear test was executed at a speed of 200 mm/min. Chemical Analysis Chemical analyses were performed on deboned breast meat (M. Pectoralis major and M. Pectoralis minor) and thigh (skin on) samples. The breast and thigh meat (skin on) samples were chilled at 4°C (±1°C) for 24 h after deboning, homogenized (DAMPA CT-35 N Bowl cutter, Golasecca (VA) Italy) for 20 s, vacuum packed, and stored at –20°C until chemical analyses were executed. Prior to each analysis, meat samples were defrosted at 4°C (±1°C) for 12 hours. The moisture and ash content (%) of the meat samples was determined by using a 2.5 g homogenized meat sample according to the Official Methods of Analysis 934.01 and 942.01, respectively (AOAC, 2002a; 2002b). A 5 g homogenized meat sample was used for the chloroform/methanol (1:2 v/v for breasts; 2:1 v/v for thighs) extraction technique as described by Lee et al. (1996) to determine the total lipid content (%). The defatted dried meat sample was used to determine the total crude protein content (%) according to the Dumas combustion method 992.15 (AOAC, 2002c) and protocol stipulated by Geldenhuys et al. (2013). Statistical Analysis All data collected in the study were subjected to the General Linear Model (GLM) procedure of SAS (SAS, 2003), and a univariate analysis of variance (ANOVA) was generated. A Shapiro-Wilk test was executed for a non-normality of residuals test (Shapiro and Wilk, 1965). Outliers were identified and removed from the data when non-normality was significant (P ≤ 0.05). Differences between treatment means were tested according to Fisher's least significant difference (LSD) test of SAS. Means with a standard error (SE) of the mean were used to present the data. A significant level of P ≤ 0.05 was used to conclude differences between means. For all the variables measured in duplicate or more, means were calculated and used in statistical analysis. RESULTS Carcass Characteristics Table 1 shows carcass characteristics of spent laying hens from different production systems. Caged hens had heavier warm and cold carcass (P ≤ 0.05), thigh and wing weights (P ≤ 0.05) and increased percentage thigh (P < 0.001) compared with free-range hens. The breast and drum percentages were higher (P ≤ 0.05) for free-range than caged hens. The gizzard weight and percentage were higher (P ≤ 0.05) for the free-range than caged hens. The non-carcass components, neck, and head, did not differ (P > 0.05) between production systems, while caged hens had heavier (P ≤ 0.001) feet. Free-range hens had heavier (P < 0.001) breast bone weights, higher (P < 0.001) bone percentages, and lower (P ≤ 0.05) meat percentages (Table 1). Table 1. Means (± SE) of carcass characteristics of caged and free-range spent laying hens. Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 1Means with n = 30 per treatment. 2Means with n = 15 per treatment. 3Calculated as a percentage of the cold carcass weight. 4Calculated as a percentage of the warm carcass weight. 5Calculated as a percentage of the right breast portion. View Large Table 1. Means (± SE) of carcass characteristics of caged and free-range spent laying hens. Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 Caged Free-range P-value Carcass composition1  Warm carcass (g) 1207.9 ± 22.91 1127.1 ± 24.16 0.018  Cold carcass (g) 1202.0 ± 22.73 1119.3 ± 23.75 0.015  Breast (g) 156.6 ± 3.89 158.7 ± 3.87 0.711  Thigh (g) 233.9 ± 5.70 206.5 ± 5.20 <0.001  Drum (g) 80.3 ± 1.88 79.2 ± 1.59 0.677  Wing (g) 99.7 ± 2.60 89.3 ± 1.48 0.001  Breast (%) 26.1 ± 0.51 28.3 ± 0.28 <0.001  Thigh (%)3 38.9 ± 0.37 36.8 ± 0.27 <0.001  Drum (%)3 13.4 ± 0.20 14.2 ± 0.20 0.004  Wing (%)3 16.6 ± 0.30 16.0 ± 0.21 0.132 Organs1  Heart (g) 8.4 ± 0.26 8.1 ± 0.19 0.356  Liver (g) 29.6 ± 1.16 26.0 ± 1.58 0.067  Gizzard (g) 30.5 ± 0.73 33.9 ± 1.04 0.009  Heart (%)4 0.7 ± 0.02 0.7 ± 0.02 0.264  Liver (%)4 2.5 ± 0.11 2.3 ± 0.13 0.325  Gizzard (%)4 2.5 ± 0.07 3.0 ± 0.02 <0.001 Non-carcass parts1  Neck (g) 50.3 ± 0.96 49.9 ± 1.06 0.786  Head (g) 55.7 ± 1.00 55.1 ± 0.98 0.642  Feet (g) 58.1 ± 1.38 51.7 ± 1.06 <0.001 Breast composition2  Meat (g) 75.0 ± 3.83 76.0 ± 3.22 0.833  Bones (g) 48.1 ± 3.37 64.3 ± 2.33 <0.001  Skin (g) 18.8 ± 1.39 18.9 ± 0.93 0.949  Meat (%)5 51.7 ± 1.35 47.3 ± 0.94 0.012  Bones (%)5 33.0 ± 1.49 40.1 ± 0.97 <0.001  Skin (%)5 13.2 ± 1.02 11.7 ± 0.39 0.204 1Means with n = 30 per treatment. 2Means with n = 15 per treatment. 3Calculated as a percentage of the cold carcass weight. 4Calculated as a percentage of the warm carcass weight. 5Calculated as a percentage of the right breast portion. View Large Physical Characteristics The effects of production systems on the physical attributes of spent laying hen meat are shown in Table 2. Free-range hens had higher (P ≤ 0.05) breast thaw and cooking loss percentages, thigh cooking loss percentages, meat redness (a*), hue angle value, skin redness (a*), and breast and thigh shear force values. Caged hens had higher (P < 0.001) thigh thaw loss percentages. Table 2. Means (± SE) of physical attributes of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 1Means with n = 12 replicates per treatment. 2Means with n = 30 replicates per treatment. View Large Table 2. Means (± SE) of physical attributes of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 Caged Free-range P-value Thaw loss (%)1  Breast 6.1± 0.48 8.0 ± 0.77 0.043  Thigh 8.5 ± 1.62 5.5 ± 0.54 <0.001 Cooking loss (%)1  Breast 12.1 ± 0.69 15.0 ± 0.96 0.023  Thigh 19.4 ± 0.93 23.5 ± 0.94 0.005 Meat pH241  Breast 6.15 ± 0.016 6.18 ± 0.022 0.322  Thigh 6.32 ± 0.022 6.31 ± 0.026 0.832 Meat color1  L* 54.51 ± 0.398 54.24 ± 0.532 0.682  a* 0.54 ± 0.222 1.40 ± 0.135 0.003  b* 8.45 ± 0.215 8.25 ± 0.171 0.468  Hue angle (°) 0.36 ± 0.229 1.30 ± 0.172 <0.001  Chroma 8.57 ± 0.213 8.41 ± 0.172 0.566 Skin color2  L* 71.74 ± 0.421 72.09 ± 0.325 0.512  a* 0.01 ± 0.089 0.53 ± 0.144 0.003  b* 7.44 ± 0.401 6.58 ± 0.330 0.102  Hue angle (°) 0.02 ± 0.130 0.36 ± 0.130 0.071  Chroma 7.52 ± 0.398 6.75 ± 0.329 0.138 Shear force1 (N)  Breast 12.37 ± 0.411 17.10 ± 0.751 <0.001  Thigh 29.68 ± 0.306 39.75 ± 0.826 <0.001 1Means with n = 12 replicates per treatment. 2Means with n = 30 replicates per treatment. View Large Chemical Composition The proximate composition of the breast (skinless) and thigh (skin on) meat of caged and free-range spent laying hens is shown in Table 3. Free-range hens showed higher (P ≤ 0.05) breast meat moisture content and lower thigh meat ash content. However, the breast ash content of the caged hens was higher (P < 0.001). Crude protein and fat of the breast and thigh meat, as well as thigh meat moisture content, did not differ (P > 0.05) between caged and free-range hens. Table 3. Means1 (± SE) of proximate composition of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 1Means with n = 12 per treatment. View Large Table 3. Means1 (± SE) of proximate composition of breast and thigh meat of caged and free-range spent laying hens. Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 Caged Free-range P-value Breast  Moisture content 73.9 ± 0.12 74.5 ± 0.19 0.036  Crude protein 21.7 ± 0.24 21.5 ± 0.31 0.699  Fat 3.8 ± 0.20 3.3 ± 0.24 0.107  Ash 1.3 ± 0.04 1.1 ± 0.02 <0.001 Thigh  Moisture content 67.3 ± 0.67 69.0 ± 0.81 0.116  Crude protein 10.0 ± 0.91 10.1 ± 0.58 0.905  Fat 21.5 ± 1.24 20.2 ± 0.77 0.389  Ash 2.0 ± 0.02 1.0 ± 0.03 0.026 1Means with n = 12 per treatment. View Large DISCUSSION Carcass Characteristics The lower carcass and portion yields for free-range spent laying hens in the present study could be ascribed to a number of factors: environmental temperatures, light intensity, diet, exercise, and pasture. All the above-mentioned factors could have interfered with growth performance of the laying hens, and hence carcass and portion yields. Moreover, the increase in the digestive tract weight of the free-range birds to adapt to high fiber in natural pastures could also negatively impact carcass weight and composition (Ponte et al., 2008; Mateos et al., 2012). To qualify as a free-range production system in South Africa, 50% of the accessible outdoor area must be covered with green grass (SAPA, 2012). The variation in the percentage yield of the portions could be attributed to the differences in the portion weights. For instance, the caged hens had heavier thighs than free-range hens, which would have led to the higher thigh and lower breast percentage. Free-range systems favor breast muscle development due to the motory behavior of the birds (Castellini et al., 2002). Access to pasture in the free-range system could be the reason for the increased gizzard weight and percentage for the free-range hens; it was noted that the hens had access to pastures that had some vegetative growth. However, it was not determined whether they had consumed some of this plant material. High dietary fiber diets stimulate gizzard muscle development in order to grind and digest feed effectively (Mateos et al., 2012). The heavier feet for caged hens could be a result of high fat and less connective tissue in the caged hen's feet. Free-range bird feet go through intensive movement and exercise, which could increase the amount of connective tissue and lower the fat and muscle content. Additionally, caged birds are prone to foot lesions due to high stocking density and the nature of the cage floors (Farhadi and Hosseini, 2016; Kiyma et al., 2016). Foot lesions could have contributed to the heavy feet of the caged hens, as they do cause foot swelling. The heavy breast bones for free-range hens could be attributed to the development of bone and cartilage of the breast in order to support muscles for the intense wing movement (Lewis et al., 1997). Although free-range hens are not flight birds, most of the times they do attempt to fly for a short distance. For instance, hens under free-range systems fly from litter to perches as avoidance behavior and to escape capture. Physical Characteristics The high thigh thaw loss of caged hens could be ascribed to the numerically high intramuscular fat content of the caged hen thighs coupled with the state of the protein. Moreover, caged hen thighs in the study had a high level of abdominal fat attached. Although water-holding capacity is more related to meat protein functional properties and pH (Bowker and Zhuang, 2015), Colmenero (2014) noted that thaw and cooling losses, which are a function of the water-holding capacity of meat, also can be influenced by meat fat content when stored and cooked. The fluctuation of environmental temperatures coupled with high average temperatures, reduces the water-holding capacity of muscles (Wang et al., 2009). Free-range hens are exposed to uncontrolled environments (as discussed previously). The aforementioned aspects could be the cause of the high thaw and cooking losses of the free-range hen meat. Castellini et al. (2002) also reported an increase in the cooking loss of the breast (indoor: 31.1 and 30.3%; free-range: 34.0 and 33.5%) and thigh (indoor: 32.7 and 31.0%; free-range: 35.2 and 34.0%) when broiler chickens were given access to free-range at 51 and 81 d of age, respectively. The cooking loss results in this study are similar to those observed by Castellini et al. (2002). However, these findings contradict those of Funaro et al. (2014). Thaw and cooking loss results in this study also pose a challenge to literature on the relationship between muscle physical as well as chemical properties and water-holding capacity. Fu et al. (2014) noted that free-range birds had larger muscle fiber diameter. A positive association exists between muscle fiber diameter and plasma creatine kinase activity, which may be revealed in protein turnover and hence in muscle growth (Funaro et al., 2014). Furthermore, free-range hens are bound to have higher collagen thickness and cross-linking owing to their higher level of motory activity (Astruc, 2014). The latter factors are expected to result in a higher water-holding capacity, hence, low thaw and cooking losses; however, this is not the case in this study, as higher thaw and cooking loss percentages were recorded for free-range hens than for caged hens (Table 2). The high thaw and cooking loss observed in the current study is detrimental to meat quality, as it may result in drier and tougher meat. The effect of production systems was not observed in the meat pH. The pH values (6.15 to 6.32) in this study were higher than the 5.8 expected, which could be attributed to the light weight of the birds and pre-slaughter handling. Michalczuk et al. (2017) explained that light birds are highly predisposed to pre-slaughter stress as they tend to struggle a lot along the slaughter lines antemortem, since they are accustomed to being active. The prolonged struggling depletes the glycogen reserves resulting in higher ultimate pH values of the meat (Honikel, 2014). Moreover, these birds were transported the previous afternoon and held overnight in a free-range holding facility (with ad lib access to water and feed, although the feed was different from what they had been fed during their production life) prior to being transported to the abattoir. If the birds had not consumed any feed during this period, their muscle glycogen reserves may have become depleted, and this would have resulted in a higher muscle pH postmortem. Nonetheless, the pH values recorded are in acceptable ranges as observed in other studies (Funaro et al., 2014; Michalczuk et al., 2017). Skin and meat color are key determinants of consumers’ acceptance of chicken meat (Barbut, 2015). According to CIE (1976), redness (a*) spans from +60 (red) to -60 (green). The use of redness (a*) to measure chicken meat color is limited, as myoglobin (the protein that determines redness of meat) is not readily detectable in chicken meat (Zhuang and Savage, 2012; Barbut, 2015). The increase in the redness (a*) of the skin of free-range compared to caged birds (Table 2) indicates undesirable pink and red tones (Ponte et al., 2008). Although most of the literature agrees that pasture imparts a desirable yellow characteristic to the skin (Fanatico et al., 2007; Michalczuk et al., 2017), Barbut (2015) noted that submerging in warm water (as in this study) results in a loss of this desirable, traditional yellowness and may even lead to the skin becoming more red. Thus, the influence of scalding could have resulted in the skin color differences between caged and free-range hens in this study. The higher redness of the muscle from the free-range hens could be ascribed to the increased motor activity, as noted by Castellini et al. (2002). The redness values of the current study show a similar trend to that as reported for the skin by Fanatico et al. (2007) (caged: -0.17; free-range: 0.44; for slow-growth genotype) and for meat by Skŕivan et al. (2015) (caged: 0.3; free-range: 1.9). Aalhus et al. (2009) noted that a strong relationship exists between muscle fiber diameter and meat tenderness with meat containing small muscle fiber diameters being more tender. Free-range systems have been reported to increase muscle development, which translates into larger fiber diameters (Fu et al., 2014; Funaro et al., 2014). Although muscle fiber diameter was not analyzed in the current study, an increase in muscle fiber diameter could be the reason for the higher shear force values recorded for both the breast and thigh meat of free-range hens. Furthermore, the motor activity of free-range birds is known to increase the amount of connective tissue and collagen cross-linkages (Astruc, 2014), which could lead to higher shear force values. Castellini et al. (2002) (breast: 20.59 N vs. 26.58 N; thigh: 28.15 N vs. 34.13 N at 81 d of age) results also showed significant higher shear force values for broiler chickens reared under free-range than indoor systems as in this study. However, there are studies in which no significant differences in shear force values of meat were recorded between free-range and caged chickens (Fanatico et al., 2005b; Wang et al., 2009). The breast shear force values (caged: 12.37 N and free-range: 17.10 N) in the current study are within range with those of broiler chickens recorded by Chen et al. (2007) (11.9 N to 17.36 N) and Hashim et al. (2013) (16.96 N to 18.63 N). Chuaynukool et al. (2007) reported spent laying hen breast meat as being tougher (30.79 N) than indigenous (22.36 N) and broiler (15.59 N) meat. The lower than expected shear force values of spent laying hen breast meat in this study could be characteristic of the lower breast weights compared to those of broiler chickens, as Lyon et al. (2010) concluded that breast weight is correlated to tenderness, with lower weights being more tender. Chemical Composition The nutrient composition (moisture, protein, fat, and ash) of spent laying hen meat recorded (Table 3) in this study are in range with those of chicken in literature by Funaro et al. (2014) (breast: moisture 73.4%; protein 23.3%; fat 1.0%; ash 1.2%; and thigh [skin on]: moisture 67.9%; protein 18.6%; fat 10.8%; and ash 1.0%) and Keeton et al. (2014) (meat: moisture 75.5%; protein 21.4%; fat 3.1%; and ash 1.0%). However, the breast meat moisture content results in the current study contradict those of Fanatico et al. (2005b) and Funaro et al. (2014). These authors found indoor broiler chicken breast meat to have higher moisture content (72.2 and 73.4%) than free-range reared broilers (71.1 and 72.5%). Keeton et al. (2014) noted that the relationship among moisture, protein, and ash is inversely proportional to the fat content of the meat. The literature generally agrees that free-range production decreases the intramuscular fat content of meat (Fu et al., 2014; Funaro et al., 2014). The reduction in intramuscular fat of the breast and thigh also was noted in the current study, although it was not significant. Based on Keeton et al. (2014), the low fat content of the breast meat of free-range hens could have resulted in the higher moisture content observed in this study. Nonetheless, other studies have reported no significant differences among the moisture, protein, fat, or ash content for free-range and caged birds (Michalczuk et al., 2014; Skŕivan et al., 2015; 2017). CONCLUSIONS Production systems had an effect on carcass characteristics and physical and chemical attributes of the meat derived from spent laying hens. The carcass and portion weights of the spent laying hens were also lower than the minimal market weights (carcass weight: 1.5 kg) of broiler chickens. This constitutes a further reason for the lower economic value of spent laying hens. The free-range production system increased the weight of the prime economic portion (breast); however, the meat percentage of the breast portion was reduced. As expected, the selected physical attributes of free-range hen meat were higher than those of caged hens, which could be attributed to increased motor activities and the uncontrolled environmental conditions experienced by the former. The skinless breast meat fat content of spent laying hens in this study was lower than that of broiler chicken breasts reported in the literature. Thus, we might recommend spent laying hen breast meat to consumers concerned about high fat content in chicken. Further studies are recommended to evaluate the fatty acids and sensory profile of the meat of spent laying hens as influenced by production systems. 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Poultry ScienceOxford University Press

Published: Mar 22, 2018

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