Dynamics of nutrient utilization, heat production, and body composition in broiler breeder hens during egg production

Dynamics of nutrient utilization, heat production, and body composition in broiler breeder hens... Abstract Changes in heat production (HP) and body composition (BC) in modern broiler breeders can provide means to understand nutrient utilization. Twelve Cobb 500 breeders were evaluated 10 times from 26 to 59 wk of age. The same wired caged breeders were moved to respiratory chambers connected to an indirect calorimetry to obtain oxygen consumption (VO2) and carbon dioxide production (VCO2), HP, and respiratory exchange ratio (RER). The same hens were evaluated for BC using a dual X-ray absorptiometry (DEXA). Data were analyzed during light (16 h) and dark (8 h) period using a mixed model to evaluate calorimetry parameters, a factorial design 2 × 10 for normalized calorimetry parameters, and Complete Randomized Design (CRD)—one way ANOVA for BC. Means were separated by Tukey-Honest Significant difference (HSD). HP increased with age (d) in 0.152 kcal/d, VO2 and VCO2 were 0.031 and 0.024 L/d per each increase in age (d), respectively. In the light period, hens consumed +17.4 L/d VO2 and produced +18.9 L/d VCO2 (P < 0.01). HP during the dark period was 84 kcal/kg0.75 and during the light period was 115 kcal/kg0.75. RER decreased with age until 43 wk and remained the same until 59 wk suggesting more fat and/or protein being oxidized at later periods of production. Lean body mass ranged from 642 to 783 g/kg during the whole study reaching the lowest at 37 and 50 wk and the highest at 26 to 33 wk (P < 0.01). Body fat ranged from 168 to 261 g/kg with the lowest at 26 to 33 wk and the highest at 50 wk of age (P < 0.01). Broiler breeder females may be catabolizing fat energy reserves from 50 wk onwards when the egg production is reduced, and HP increased at 54 and 59 wk (P < 0.01) due to higher energy required for maintenance of a higher lean mass structure. Broiler breeders change nutrient fuel use during egg production. Indirect calorimetry and DEXA can be used to pursue further feed strategies to maximize egg production and maintain a healthy breeder. INTRODUCTION The continuously growing market of broiler protein for the world population requires an increase in the number and efficiency of broiler breeders. Broiler breeders have been intensively selected for growth rate, feed efficiency, and breast meat yield traits for the performance of their progeny. The reproductive traits of the current broiler breeder have advanced at a lower rate compared to the table egg production (EP) hens. For example, the average egg increase for a broiler breeder at 65 wk was 0.80 egg/yr (Cobb Supplement 2013 vs 2005) vs. 14 eggs/yr for the table-egg hens. These 14 eggs increment in the layers is due to the increase of 1 egg/yr at 80 wk, and the increase of the production cycle to 110 wk (Hy-Line Brown Commercial Layers supplement 2016 vs 2006). Broiler breeders have not increased their production cycle length, but they have improved the number of eggs per year and the broiler performance. Management and nutrition of the broiler breeder is the most complex piece of poultry production (Kleyn, 2013) because EP from parent stock and meat production for their progeny are desired traits in the poultry industry. Understanding the dynamics of heat production (HP) and body composition along with EP can provide insights of nutrient utilization but the information is lacking for the modern broiler breeder. Heat production can be measured by indirect calorimetry and by difference between ME intake (MEI) and retained energy (Sakomura, 2004). Body composition can be different at the same body weight (BW) affecting the onset of sexual maturity, so the analysis of lean and fat mass is important (Wilson et al., 1989). Body composition has changed over time resulting in leaner breeders with total protein content being very important at the onset of sexual maturity (De Beer and Coon, 2007). Salas et al. (2012) evaluated the body composition of broiler breeders using dual energy X-ray absorptiometry (DEXA) and reported a decrease in lean mass at 35 and 45 wk of age during production. Vignale et al. (2016) reported that the highest protein degradation rate in pectoralis major breast muscle occurred at 30 to 37 wk of age in broiler breeders. The large increase in degradation rate helps explain the decrease in lean mass at 35 wk reported by Salas et al. (2010). Indirect calorimetry measures volume of oxygen consumption (VO2) and volume of carbon dioxide production (VCO2) to estimate HP. The ratio VCO2/VO2 indicates the nutrient utilization and is called the respiratory exchange ratio (RER). The values for RER are 1.0, 0.74, and 0.70 for carbohydrate, protein, and fat oxidation, respectively, in birds (McLean and Tobin, 1987) and a balanced poultry feed would be a mix of the RER values. Indirect calorimetry can provide data on nutrient oxidation and the DEXA can provide body composition data to understand tissue synthesis and degradation and the dynamics of nutrient utilization in broiler breeder hens. The objectives of the present study are to study the same breeders during production from 26 to 59 wk of age: 1) to evaluate changes in calorimetry parameters with age: VO2, VCO2, RER, and HP, and 2) to determine changes in body composition with age: lean mass, fat mass, and bone mineral content (BMC). MATERIALS AND METHODS All management practices and procedures were approved by the University of Arkansas Institutional Animal Care and Use Committee # 13002. Hens and Housing A total of 12 parent stock females from Cobb 500 fast feathering (Cobb Vantress, Siloam Springs, AR) were selected from a population of 70 hens at 23 wk of age. Hens were selected to represent a normal BW population with an average BW of 2544 g ± 258 SD (10% CV). Hens were transferred from floor pens to breeder wire cages (47 cm high, 30.5 cm wide, 47 cm deep) equipped with an individual feeder and nipple drinker. The photoperiod was 16L: 8D from 26 to 59 wk. The same 12 hens were evaluated in respiratory chambers and with the DEXA 10 different times during production (26, 30, 33, 37, 40, 43, 45, 50, 54, and 59 wk of age). Hens were moved to respiratory chambers for 24 h before each evaluation to acclimate the breeders to the chambers. The hens were only acclimated for 24 h prior to evaluation because the hens were maintained in wire cages with similar dimensions and floor type to the respiratory chambers. The breeder cage also contained a similar drinker and feeder system compared to the respiratory chambers. The acclimation period was adequate because breeder hen behavior, feed consumption time, and EP remained normal performance with the Cobb 500 breeder guide, 2013). Temperature was kept at 21°C through production (Cobb 500, 2008) in cages and respiratory chambers. Egg production was recorded daily and averaged for 12 hens at every week of evaluation. Respiratory Chambers Respiratory chambers were made from polycarbonate plastic glass (61 cm long × 51 cm wide × 56 cm high) and equipped with 1 feeder and 1 nipple drinker according to the specifications of FASS 2010 (Champaign, IL). The environmental condition of the room for the respiratory chambers was the same as the metabolic cages. The room for the metabolic chambers was equipped with 2 heating and air conditioning units. These units were controlled by a Honeywell programmable thermostat that automatically switches between cooling and heating within a 2°C range. Minimum ventilation was provided by 2 ventilation fans that exhaust to the outside and draw fresh air from the hall. Each ventilation fan was controlled by a timer. The on/off cycle was adjusted as needed to maintain room air quality and desired CO2 levels. To control humidity, the room was equipped with 2 de-humidifiers (GE, Madison, WI) that remained running continuously. Relative humidity (RH) was kept at 80% (range 70 to 90%) depending on the RH of the environment. Temperature inside the chamber was 21°C (range 19 to 23°C). The room temperature was 16°C, which is 5°C lower than temperature inside the chambers to ensure the temperature inside the respiratory chambers stayed at 21°C. The indirect calorimetry system provided air flow of 12 to 15 L/min depending on the size of the hen. Delta carbon dioxide, ΔCO2 (CO2 out –CO2 in), was between 0.30 and 0.50. The gas evaluations in each chamber were measured every 12 min making 5 readings per hour and 120 readings in 24 h. The daily gas evaluation was composed of 67% during the light time (3 am to 6 pm) and 33% during the dark time (7 pm to 3 am). Diet and Feed Program Hens were fed a commercial crumbled feed during evaluation (Cobb-Vantress, Siloam Springs, AR). The breeder diet, which was provided from 22 to 58 wk of age, was formulated to have 2920 kcal/kg of ME with 15.5% crude protein. Four batches of diet were received during the 38-wk period and analyzed for proximal analysis on arrival (Table 1). Feed and energy allowance was 123 g (359 kcal/d) at 26 wk and 134 g (390 kcal/d) at 30 wk (peak production). This caloric intake was lower than Cobb's suggested value but it was used to account for the reduced energy expenditure of individually caged hens (Reyes et al., 2011, 2012). The 390-kcal ME peak feed was determined to be the requirement for breeders in cages by Salas et al. (2010). The group was fed the same amount for the 38-wk study to avoid the introduction of additional variables with the feed withdrawal period. Hens were individually fed every day at 7 am in cages and chambers. The feed was cleaned up after approximately 1 h. Fresh water was provided ad libitum during evaluation. Table 1. Composition and nutrient calculations (g/100 g as fed) of the diet. Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 1(HMTBa Met) 2-hydroxy-4-methylthio-butanoic acid. 2Supplied per kilogram of diet: vitamin A, 10,582 IU; vitamin D3, 5291 IU; vitamin E, 53 IU; vitamin B12, 0.024 mg; biotin, 0.26 mg; menadione, 2.65 mg; thiamine, 2.65 mg; riboflavin, 15.9 mg; pantothenic acid, 26.5 mg; pyridoxine, 5.29 mg; niacin, 59.5; folic acid, 2.6 mg, choline chlorine, 1543 mg. 3Supplied per kilogram of diet: Mn,100 mg; Zn, 110 mg; Fe, 48 mg; Cu, 13 mg, I, 2 mg; Se, 0.30 mg. View Large Table 1. Composition and nutrient calculations (g/100 g as fed) of the diet. Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 1(HMTBa Met) 2-hydroxy-4-methylthio-butanoic acid. 2Supplied per kilogram of diet: vitamin A, 10,582 IU; vitamin D3, 5291 IU; vitamin E, 53 IU; vitamin B12, 0.024 mg; biotin, 0.26 mg; menadione, 2.65 mg; thiamine, 2.65 mg; riboflavin, 15.9 mg; pantothenic acid, 26.5 mg; pyridoxine, 5.29 mg; niacin, 59.5; folic acid, 2.6 mg, choline chlorine, 1543 mg. 3Supplied per kilogram of diet: Mn,100 mg; Zn, 110 mg; Fe, 48 mg; Cu, 13 mg, I, 2 mg; Se, 0.30 mg. View Large Body Composition Analysis Hens were scanned the previous day before evaluation in the respiratory chambers using a DEXA scanner (GE) with a small animal body software module (Lunar Prodigy from GE encore version 12.2). Green lights were set up in the DEXA room to help keep the hens calm while scanning for about 3.5 to 4 min per hen. No chemicals or anesthesia was used and hens were scanned at the same time (around 1 pm) at every point of evaluation. Hens were returned to the respiratory chambers after scanning. Total tissue, lean mass, fat mass, and BMC were adjusted to body composition values analyzed by chemical analysis using equations previously developed by Salas et al. (2012). Calculation Data from indirect calorimetry were separated as time of day (light or dark) and averaged within a day. VO2, VCO2, and RER (VCO2/VO2) were calculated as liters per day (L/d) for the development of the mixed model and normalized to metabolic BW (L/kg BW0.75) for comparative purposes. Heat production was obtained using the Brouwer equation: HP kcal/d = 3.866 VO2 L/d + 1.233 VCO2 L/d (MacLean and Tobin, 1987). Heat production was calculated as kcal/d and kcal/kg0.75. The body composition was reported as g and g/kg: lean, fat, and BMC. Tissue gain (g/d) was calculated over the period between 2 proximate ages evaluated. For example, 10.5 g/d of lean tissue was BW 30 wk – BW 26 wk divided by the number of days between these 2 ages, and the same calculations for the next periods (g/d). Statistical Analysis A mixed model was used to evaluate calorimetry parameters: HP (kcal/d), VO2 (L/d), VCO2 (L/d) with age (d), BW (kg), and time of day (2 levels: light and dark) as fixed effects. The breeder hen was considered a random effect being the hens were measured repeatedly at every age. For normalized calorimetry data (kcal/kg BW0.75 and L/kg BW0.75), a 2 × 10 factorial design (time of day × age) was analyzed. The body composition data were analyzed by a complete randomized design utilizing one-way ANOVA (age) with hen as random effect. Means were separated by the Tukey-HSD test. Fat gain (X) was fitted against Lean gain (Y) in a simple linear regression. P-value was considered significant when P ≤ 0.05. All analyses were determined with JMP12 (SAS, 2015). RESULTS Calorimetry Parameters Heat production or heat expenditure is the result of indirect calorimetry evaluation: volume of oxygen consumption (VO2) and carbon dioxide production (VCO2). The HP was measured during the EP cycle of the broiler breeder. A mixed model provided the opportunity to understand the dynamics of VO2, VCO2, and HP by age and time of day (light and dark periods) with repeated measurements such as the case of the present study where the same hen was evaluated at every point of evaluation. Gases and HP were increased as the age increased from 26 to 59 wk: 0.031 L/d VO2, 0.024 L/d VCO2, and 0.15 kcal/d HP (P < 0.01) (Table 2). At the end of the 38-wk study (59 wk of age of the breeder), HP was the highest because of a gain in body tissue that was mainly lean mass gain during the 45- to 59-wk period of the production cycle. Breeder hens consumed +17.4 L/d more oxygen, produced +18.9 L/d more carbon dioxide, and produced + 89.8 kcal/d more heat during the light period (3 am to 6 pm) compared to the dark period (7 pm to 2 am) during the 38-wk study. The increase in HP during the light time is because of higher activity and metabolic processes that occur during this time. The VO2, VCO2, and HP parameter estimates of the mixed model provide half of this difference (8.7 VO2/d, 9.4 VCO2/d, and 44.9 kcal/d), respectively (Table 2), due to 2 periods being evaluated (light and dark). VO2 was always higher than VCO2 in the light and dark periods (Table 3). The interaction effect of time of day and age was not significant (P > 0.05) when VO2, VCO2, and HP were expressed based on BW (L/kg BW0.75 and kcal/kg BW0.75) (Table 3). The breeder hens based on their metabolic BW consumed 27% more VO2 (6.1 L/kg BW0.75), produced 30% more VCO2 (6.5 L/kg BW 0.75), and 27% more HP (31 kcal/kg BW0.75) (P < 0.01) during the light period compared to the dark period. The RER was also higher during the light period (0.955 vs. 0.907) (P < 0.01) compared to the dark period meaning there are differences in nutrient utilization between light and dark periods (Table 3, Figure 1). At the end of the 38-wk production period, 59-wk-old hens had increased oxygen consumption (L/kg BW0.75) compared to <50-wk-old hens with exception of 30-wk-old hens during peak production (P < 0.01). The VCO2 production (L/kg BW0.75) was the highest at 59 wk compared to younger ages other than 26, 30, and 37 wk of age (P < 0.01). Heat production (kcal/kg BW0.75) was significantly increased with 59-wk-old hens (106 kcal/kg BW0.75) compared to previous younger ages, except for breeder hens at 30 wk of age. Breeder hens at 30 wk of age had higher VO2 consumption and VCO2 production because the breeders were at peak EP. Respiratory exchange ratio was the lowest at 43 wk of age (P < 0.01) compared to other ages, except breeders 40 and 50 wk of age. The highest RER was found at 30 wk compared to other ages except 26 wk (P < 0.01). Figure 1. View largeDownload slide Respiratory exchange ratio (RER) during daily light and dark time period for 26- through 59-wk-old broiler breeders. Factorial design 2 × 10 (time of day × age). Levels (a, b, c, d) not connected by same letter are significantly different between ages for both light and dark period, Tukey-HSD test P < 0.05. P-values: time of day P < 0.01, age P < 0.01, Time of day × age = 0.673. Figure 1. View largeDownload slide Respiratory exchange ratio (RER) during daily light and dark time period for 26- through 59-wk-old broiler breeders. Factorial design 2 × 10 (time of day × age). Levels (a, b, c, d) not connected by same letter are significantly different between ages for both light and dark period, Tukey-HSD test P < 0.05. P-values: time of day P < 0.01, age P < 0.01, Time of day × age = 0.673. Table 2. Mixed model for volume of oxygen consumption (VO2), carbon dioxide production (VCO2), and heat production (HP) for broiler breeders from 26 to 59 wk of age. Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 View Large Table 2. Mixed model for volume of oxygen consumption (VO2), carbon dioxide production (VCO2), and heat production (HP) for broiler breeders from 26 to 59 wk of age. Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 View Large Table 3. Calorimetry parameters VO2 L/kg0.75, VCO2 L/kg0.75, and HP kcal/kg0.75 for broiler breeders from 26 to 59 wk of age. 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 Levels (a, b, c, d) not connected by same letter within the columns are significantly different. 1VO2 = volume of oxygen consumption L/kg0.75/d. 2VCO2 = volume of carbon dioxide production L/kg0.75/d. 3HP = heat production kcal/kg0.75/d. 4RER = respiratory exchange ratio. 5SEM = standard error mean. View Large Table 3. Calorimetry parameters VO2 L/kg0.75, VCO2 L/kg0.75, and HP kcal/kg0.75 for broiler breeders from 26 to 59 wk of age. 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 Levels (a, b, c, d) not connected by same letter within the columns are significantly different. 1VO2 = volume of oxygen consumption L/kg0.75/d. 2VCO2 = volume of carbon dioxide production L/kg0.75/d. 3HP = heat production kcal/kg0.75/d. 4RER = respiratory exchange ratio. 5SEM = standard error mean. View Large Body Composition For body composition evaluation, a CRD design provides differences in tissue composition between ages (Table 4). Total mass that is equivalent to scale BW was higher at 50, 54, and 59 wk compared to 26, 30, 33, 37, and 40 wk (P < 0.01). Lean mass was the highest at 59 wk (3031 g) compared to 26, 37, and 50 wk (P < 0.01). The lowest lean mass was found at the beginning of production at 26 wk of age compared to 33, 40, 43, 54, and 59 wk. The absolute lean mass for breeder hens at 37, 45, and 50 wk was not different from the 26-wk-old hen (P < 0.01). Fat mass was the highest at 50 wk compared to other ages except 54 wk. The smallest amount of fat was found to be at the beginning of production (26 wk) compared to hens older than 37 wk (P < 0.01). The BMC reached the highest point at 50 wk (187 g) compared to other ages except 37, 45, 54, and 59 wk (P < 0.01). The smallest amount of BMC was at 30 wk compared to 50 wk. Body composition expressed as g/kg provides meaningful information about the relative body composition between ages (Figure 2). Lean mass (g/kg) was the highest at 26, 30, 33, and 40 wk of age and the lowest at 50 wk compared to other ages except 45 and 54 wk of age. Lean mass (g/kg) shows the first low point at 37 wk compared to the initial body composition (26 wk), and the second lowest point at 50 wk. Lean mass tends to decrease from peak until 50 wk and then increase after 50 wk. Fat mass (g/kg) was the lowest at the beginning of production and it increased gradually becoming significant after 43 wk. The largest amount of fat (g/kg) was found at 45, 50, and 54 wk (P < 0.01). Fat composition tends to increase with age reaching the highest point at 50 wk but drops after and being significantly lower at for 59 wk old, end of the present study (Figure 2). The BMC (g/kg) was higher at 50 wk compared to 33 and 40 wk (P < 0.01). Lean gain (g/d) was variable during the EP cycle and the values ranged from –6.5 g/d during 30 to 37 wk to +10.4 g/d during 26 to 30 wk. Lean gain at 37 wk was significantly lower compared to 30 and 40 wk hens (P < 0.01) suggesting protein tissue being oxidized during this period. Lean tissue was also negative at 50 wk compared to 30 and 40 wk (P < 0.01). Fat gain (g/d) was the highest at 37 and 50 wk compared to 40, 54, and 59 wk (P < 0.01). Figure 3 depicts the linear relationship between fat tissue gain and protein tissue gain. For every daily gram of lean gain, fat gain decreased 0.45 g/d during 26 to 59 wk old. Figure 2. View largeDownload slide Lean and fat body mass g/kg of broiler breeders from 26 to 59 wk of age. Graph above: body lean mass g/kg. Graph below: body fat mass g/kg. Levels (a, b, c, d, e, f) not connected by same letter are significantly different, Tukey-HSD test P < 0.05. Figure 2. View largeDownload slide Lean and fat body mass g/kg of broiler breeders from 26 to 59 wk of age. Graph above: body lean mass g/kg. Graph below: body fat mass g/kg. Levels (a, b, c, d, e, f) not connected by same letter are significantly different, Tukey-HSD test P < 0.05. Figure 3. View largeDownload slide Linear regression between fat tissue gain g/d vs. lean tissue gain g/d. Fat gain g/d = 2.811 – 0.45 × lean gain g/d; intercept P < 0.01; slope P < 0.01; R2 = 0.68; RMSE = 3.6. Figure 3. View largeDownload slide Linear regression between fat tissue gain g/d vs. lean tissue gain g/d. Fat gain g/d = 2.811 – 0.45 × lean gain g/d; intercept P < 0.01; slope P < 0.01; R2 = 0.68; RMSE = 3.6. Table 4. Body composition and tissue gain for broiler breeders from 26 to 59 wk of age. Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Levels (a, b, c, d, e, f) not connected by same letter within columns are significantly different. 1Total mass = body weight. 2BMC = bone mineral content. 3SEM = standard error mean. View Large Table 4. Body composition and tissue gain for broiler breeders from 26 to 59 wk of age. Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Levels (a, b, c, d, e, f) not connected by same letter within columns are significantly different. 1Total mass = body weight. 2BMC = bone mineral content. 3SEM = standard error mean. View Large DISCUSSION Calorimetry Parameters and EP The amount of VO2 and VCO2 for modern broiler breeders is rarely reported. Past research with meat-type breeders reports 14.6 L/kg BW0.75 for oxygen consumption (Waring and Brown, 1965), which is lower than the 20 L/kg BW0.75 value reported in the present experiment. This may be due to modern breeders having more lean tissue than breeders in 1965 when compared on a metabolic BW basis (L/kg BW0.75). The increase in VO2 in broiler breeders in the present study represents a 37% increase in oxygen consumption compared to breeder VO2 from 1965 accounting for an increase of 0.74 L/kg BW0.75 of oxygen per year. It is well known that breast yield is higher in progeny from modern high-yielding broiler breeders and the progeny genetic potential for increased lean mass is higher than before (Havenstein et al., 2003). When compared to broilers, broiler breeders have a lower VO2 and VCO2 (L/kg BW0.75) (Fedde et al., 1998). This author reported 42 L/kg BW0.75 VO2 and 40 L/kg BW0.75 VCO2 in broilers with 1.38 kg BW at 35 d, which is almost twice the amount of VO2 and VCO2 found in breeders (20 L/kg BW0.75). The increased quantitative amount of gases for broilers reported by Fedde et al. (1998) agrees with data reported by Caldas et al. (2016). The reason there is an increased oxygen consumption and carbon dioxide production in modern broilers compared to broiler breeders is because of the high growth rate and ad libitum feed consumption for broilers while breeder hens are fed restricted amounts of feed during EP to avoid over weight hens. Heat production is considered to be a measure of energy use for maintenance, activity, and heat increment. Metabolizable energy for maintenance (MEm) was evaluated during fasting period, so no activity and no heat increment of feeding were included in the measurement. Maintenance energy is the highest proportion of ME needed by the modern breeder hen accounting for 79% of the energy intake at peak EP at normal temperature, 21°C (Reyes et al., 2011). The MEm has been reported to be 88 kcal/kg0.75/d Hubbard meat type in broiler breeders (Spratt et al., 1990a,b) and 98.3 kcal/kg0.75/d with Cobb500 genetics at 21°C (Reyes et al., 2011, 2012). There is little research that reports HP values per se from broiler breeders using calorimetry systems, so comparisons become complicated. In the present experiment, HP has been measured during light and dark times and resulted in 115 and 84 kcal/kg0.75/d, respectively. The HP in the dark period is similar to the MEm reported by previous authors, because the HP in the dark period does not account for activity and heat increment because hens were fed 12 h earlier. Determining the difference of 31 kcal/kg0.75/d between the light and dark period is the energy of activity and heat increment during the light period. The determination of MEm was not the main focus of this study but HP accounts for a high percentage of maintenance. The highest HP of 106 kcal/kg0.75/d was at 59 wk of age (end of the study) compared to 100 kcal/kg0.75/d at the beginning of lay, 26 wk. The increased HP caused by an increase in lean mass in the 59-wk breeder while fat tissue was decreasing suggests the hen is using fat calories to maintain the higher BW achieved at the end of the experiment. Protein synthesis produces more HP due to protein using more oxygen than fat synthesis (Teeter et al., 1996). This author showed that the oxygen required per unit protein synthesized was 380% greater than for fat. Another measurement that provides energy utilization is RER. It provides means to differentiate nutrient utilization between carbohydrates, protein, and fat because these are the only nutrients assumed to release energy for maintenance of life in the human and animals (McLean and Tobin, 1987). The RER for the oxidation of carbohydrates, protein, and fat in chickens is 1.0, 0.74, and 0.70, respectively (MacLean and Tobin, 1987). Because the breeder diet is a balance of carbohydrates, proteins, and fats, the RER data can only be compared between ages. RER reached the lowest point at 40 to 43 wk of age that could mean more fat and/or protein oxidation is occurring at that time compared to carbohydrate utilization at the beginning of production. The breeder RER decreases at 45 wk and remains low suggesting the hens were using less carbohydrates at 45 wk compared to 30 wk at peak production. Salas et al. (2017) used stable isotopes and reported broiler breeder utilized glucose for egg lipid formation at the beginning of production and mobilized dietary fat for egg lipid synthesis at the end of production. Salas and group findings are in partial agreement with the results in the present experiment. High RER variability was seen during egg oviposition times and during day time but the RER data were less variable during the night when activity was decreased. The observed RER differences between hens during the light period may require a different mechanistic model to explain breeder hen's behavior during EP. Additional RER data for breeders in production are needed to help understand the significance of this value and to determine if RER may change with feeding strategies, individual bird variation, and genetics. Body Composition, and EP Lean tissue mass (g and g/kg BW) reached the lowest point at 37 and 50 wk that is in full agreement with the data found by Salas et al. (2010) and Vignale et al. (2016). Vignale and group used 15N phenylalanine to calculate the fractional protein synthesis and degradation rate and found the highest protein degradation rate for pectoralis major was at peak production (30 to 37 wk). The authors suggested the hen utilized breast protein turnover to support EP. These results are in agreement with the negative lean tissue gain found at 37 wk in the present study but the negative tissue lean gain was different only compared to 30 and 43 wk of age breeders and not to other ages because of high variability between hens. After 50 wk of age, EP is decreasing and the hen starts increasing lean tissue. Breeder hens older than 50 wk breeder may be preparing body composition for the next clutch or production cycle as it happens in nature. Lean mass was high at the beginning of production (24 wk) that matches with high fractional protein synthesis rate prior to sexual maturity shown by Vignale et al. (2016). Van Emous et al. (2015) reported breast muscle amount of 17.24% at 35 wk compared to 20.15% at 22 wk and 16.43% at 59 wk. These findings are in partial agreement with the present study. Van Emous and group reported less breast muscle at 35 wk similar to the present study but did not observe an increase in lean mass at 59 wk as found it here. The authors also observed different pattern for fat deposition in their breeder hens compared to present study. The authors suggested abdominal fat increased with age and was the highest at termination of the production period. The authors used a different modern genetic line than the Cobb 500FF as used in the present study that may be the cause of the disagreement. Fat utilization is important in egg lipid formation (Boonsinchai et al., 2016), and a balance of protein and fat utilization exists during the complex EP process. In the present study, fat mass increased with age until 50 wk of age and then body fat mass and % fat declined through 59 wk (termination of study). Body fat utilization for the purpose of supporting EP may not be as important as lean tissue utilization because lean mass decreases when the hen is at peak EP. This is in contrast to fat accumulation that occurs throughout peak production and reaches the highest fat mass and percent fat at 50 wk of age. After 50 wk of age, fat mass and % fat decrease to support the additional maintenance calorie needs of breeders that gain lean mass during the last 1/3 of the production period. The dynamic pattern of breeder fat mass and lean mass change with age observed in present study matches very closely to previous reports by Salas et al. (2010) and Vignale et al. (2016). Bone mineral content is the lowest at peak production (30 wk) compared to 50 wk. Because Ca and P account for 23% and 20% of the BMC, respectively (Caldas, 2015), data suggest high utilization of minerals for egg shell formation during peak production. After 50 wk of age, broiler breeder EP is reduced to less than 50% thus allowing minerals and BMC to increase. Egg production in this experiment was close to the standard (Cobb, 2013). Heat production and body composition change with age but the change along EP is more important because the objective of meat-type breeders is to produce chicks of high quality by producing good quality eggs. Both EP and HP start low at the beginning of the EP (26 wk); peak production was reached at 30 wk and gradually decreased until the end of production (59 wk). Heat production is an inefficient process in terms of EP because it is mostly used for maintenance energy requirement (Chwalibog and Thorbek, 1992; Reyes et al., 2011). Lean mass and EP both increase when going from first egg to peak production, but at peak of production lean tissue tends to drop and EP gradually declines. When lean mass increases after 50 wk of age, EP keeps dropping. Respiratory exchange ratio tends to decrease as EP decreases until 43 wk of age, then RER increases when EP drops after 43 wk. In summary, indirect calorimetry and DEXA can be utilized as tools to better understand why breeders use specific fuel from feed nutrients and body tissue to develop better feeding strategies for feeding the pullet and breeder for maximum production of quality chicks. Acknowledgements The authors acknowledge Cobb-Vantress, Inc. for donating the hens and feed for the present study. REFERENCES Boonsinchai N. K. H. , Mullenix G. , Caldas J. V. , England J. A. , Coon C. N. . 2016 . De novo lipogenesis in broiler breeder hens . 187 – 189 in 5th EAAP Publication 137 . Skomial J. , Lapierre H. , eds. Wageningen Academic Publishers , Krakow, Poland . Caldas J. V. 2015 . Calorimetry and body composition research in broilers, and broiler breeders . PhD Diss. Univ. Arkansas, AR, USA . Caldas J. V. , Hilton K. , Boonsinchai N. , Schlumbohm M. , England J. A. , Coon C. N. , 2016 . Dynamics of nutrient utilization, heat production and body composition in broiler breeder hens during egg production. 5th EAAP International Symposium on Energy and Protein Metabolism and Nutrition . 357 – 358 in EAAP Publication No. 137 . Skomial J. , Lapierre H. , eds. Wageningen Academic Publishers , Krakow, Poland . Chwalibog A. , Thorbek G. . 1992 . Note about calculation of oxidation of nutrients in pigs . Physiol. Nutr . 67 : 83 – 86 . Google Scholar CrossRef Search ADS Cobb 500 breeder guide . 2005, 2008, and 2013 . Breeder Management Supplement . Cobb-Vantress Inc. , Siloam Springs AR. USA . De Beer M. , Coon C. N. . 2007 . The effect of different feed restriction programs on reproductive performance, efficiency, frame size, and uniformity in broiler breeder hens . Poult. Sci. 86 : 1927 – 1939 . Google Scholar CrossRef Search ADS PubMed Fedde M. R. , Weigle G. E. , Wideman R. F. . 1998 . Influence of feed deprivation on ventilation and gas exchange in broilers: relationship to pulmonary hypertension syndrome . Poult. Sci. 77 : 1704 – 1710 . Google Scholar CrossRef Search ADS PubMed Federation of Animal Science Societies. FASS . 2010 . Guide for The Care and Use of Agricultural Animals in Research and Teaching . 3rd edition . Champaign, IL . Havenstein G. B. , Ferket P. R. , Qureshi M. A. . 2003 . Carcass composition and yield of 1957 versus 2001 when fed representative 1957 and 2001 broiler diets . Poult. Sci. 82 : 1500 – 1508 . Google Scholar CrossRef Search ADS PubMed Hy-Line 2006-2008 . 2016 . 1 – 3 , Brown Commercial Layers, Management Guide . Hyline, www.hyline.com . JMP®, Version 12 . 1989–2015 . SAS Institute Inc. , Cary, NC . Kleyn R. 2013 . Chicken Nutrition . 21 – 42 in A Guide for Nutritionists and Poultry Professionals . British library press , Leicestershire, London, UK . McLean J. A. , Tobin G. . 1987 . Animal and human calorimetry . 1 – 49 in The oxidation of Foodstuffs and Excreta . Cambridge University press , UK . Google Scholar CrossRef Search ADS Reyes M. E. , Salas C. , Coon C. N. . 2011 . Energy requirement for maintenance and egg production for broiler breeder hens . Int. J. Poult. Sci. 10 : 913 – 920 . Google Scholar CrossRef Search ADS Reyes M. E. , Salas C. , Coon C. N. . 2012 . Metabolizable energy requirements for broiler breeder in different environmental temperatures . Int. J. Poult. Sci. 11 : 453 – 461 . Google Scholar CrossRef Search ADS Sakomura N. K. 2004 . Modeling energy utilization in broiler breeders, laying hens and broilers . Bras. J. Poult. Sci. 6 : 1 – 11 . Google Scholar CrossRef Search ADS Salas C. , Ekmay R. D. , England J. , Cerrate S. , Coon C. N. . 2010 . Energy requirement of broiler breeder hens with different body weights . 635 – 636 in Energy and Protein Metabolism and Nutrition . The 3rd EAAP International Symposium on Energy and Protein Metabolism and Nutrition. EAAP publication no. 127 . Crovetto G. M. , ed. Parma, Italy . September 6–10, 2010 . Salas C. , Ekmay R. D. , England J. , Cerrate S. , Coon C. N. . 2012 . Determination of chicken body composition measured by dual energy X-ray absorptiometry . Int. J. Poult. Sci. 11 : 462 – 468 . Google Scholar CrossRef Search ADS Salas C. , Ekmay R. D. , England J. A. , Cerrate S. , Coon C. N. . 2017 . Mechanisms of lipid mobilization towards egg formation in broiler breeder hens using stable isotopes . Poult. Sci. 96 : 383 – 387 . Google Scholar CrossRef Search ADS PubMed Spratt R. S. , McBride B. W. , Bayley H. S. , Leeson S. . 1990a . Energy metabolism of broiler breeder hens: 1. The partition of dietary energy intake . Poult. Sci. 69 : 1339 – 1347 . Google Scholar CrossRef Search ADS Spratt R. S. , McBride B. W. , Bayley H. S. , Leeson S. . 1990b . Energy metabolism of broiler breeder hens.: 2. Contribution of tissues to total heat production in fed and fasted hens . Poult. Sci. 69 : 1348 – 1356 . Google Scholar CrossRef Search ADS Teeter R. G. , Wiernusz C. J. , Belay T. . 1996 . Animal nutrition in the 21st century. A poultry perspective . Anim. Feed Sci. Technol. 58 : 37 – 47 . Google Scholar CrossRef Search ADS Van Emous R. A. , Kwakkel R. P. , van Krimpen M. M. , Hendriks W. H. . 2015 . Effects of dietary protein levels during rearing and dietary energy levels during lay on body composition and reproduction in broiler breeder females . Poult. Sci. 5 : 1030 – 1042 . Google Scholar CrossRef Search ADS Vignale K. , Caldas J. V. , England J. A. , Boonsinchai N. , Sodsee P. , Putsakum M. , Pollock E. D. , Dridi S. , Coon C. N. . 2016 . The effect of four different feeding regimens from rearing period to sexual maturity on breast muscle protein turnover in broiler breeder parent stock . Poult. Sci. 96 : 1219 – 1227 . Waring J. J. , Brown W. O. . 1965 . A respiration chamber for the study of energy utilization for maintenance and production in the laying hen . J. Agric. Sci. 65 : 139 . Google Scholar CrossRef Search ADS Wilson H. R. , Ingram D. R. , Mather F. B. , Harms R. H. . 1989 . Effect of daily restriction and age at initiation of a skip-a-day program for young broiler breeders . Poult. Sci. 68 : 1442 – 1446 . 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

Dynamics of nutrient utilization, heat production, and body composition in broiler breeder hens during egg production

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© 2018 Poultry Science Association Inc.
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0032-5791
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10.3382/ps/pey133
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Abstract

Abstract Changes in heat production (HP) and body composition (BC) in modern broiler breeders can provide means to understand nutrient utilization. Twelve Cobb 500 breeders were evaluated 10 times from 26 to 59 wk of age. The same wired caged breeders were moved to respiratory chambers connected to an indirect calorimetry to obtain oxygen consumption (VO2) and carbon dioxide production (VCO2), HP, and respiratory exchange ratio (RER). The same hens were evaluated for BC using a dual X-ray absorptiometry (DEXA). Data were analyzed during light (16 h) and dark (8 h) period using a mixed model to evaluate calorimetry parameters, a factorial design 2 × 10 for normalized calorimetry parameters, and Complete Randomized Design (CRD)—one way ANOVA for BC. Means were separated by Tukey-Honest Significant difference (HSD). HP increased with age (d) in 0.152 kcal/d, VO2 and VCO2 were 0.031 and 0.024 L/d per each increase in age (d), respectively. In the light period, hens consumed +17.4 L/d VO2 and produced +18.9 L/d VCO2 (P < 0.01). HP during the dark period was 84 kcal/kg0.75 and during the light period was 115 kcal/kg0.75. RER decreased with age until 43 wk and remained the same until 59 wk suggesting more fat and/or protein being oxidized at later periods of production. Lean body mass ranged from 642 to 783 g/kg during the whole study reaching the lowest at 37 and 50 wk and the highest at 26 to 33 wk (P < 0.01). Body fat ranged from 168 to 261 g/kg with the lowest at 26 to 33 wk and the highest at 50 wk of age (P < 0.01). Broiler breeder females may be catabolizing fat energy reserves from 50 wk onwards when the egg production is reduced, and HP increased at 54 and 59 wk (P < 0.01) due to higher energy required for maintenance of a higher lean mass structure. Broiler breeders change nutrient fuel use during egg production. Indirect calorimetry and DEXA can be used to pursue further feed strategies to maximize egg production and maintain a healthy breeder. INTRODUCTION The continuously growing market of broiler protein for the world population requires an increase in the number and efficiency of broiler breeders. Broiler breeders have been intensively selected for growth rate, feed efficiency, and breast meat yield traits for the performance of their progeny. The reproductive traits of the current broiler breeder have advanced at a lower rate compared to the table egg production (EP) hens. For example, the average egg increase for a broiler breeder at 65 wk was 0.80 egg/yr (Cobb Supplement 2013 vs 2005) vs. 14 eggs/yr for the table-egg hens. These 14 eggs increment in the layers is due to the increase of 1 egg/yr at 80 wk, and the increase of the production cycle to 110 wk (Hy-Line Brown Commercial Layers supplement 2016 vs 2006). Broiler breeders have not increased their production cycle length, but they have improved the number of eggs per year and the broiler performance. Management and nutrition of the broiler breeder is the most complex piece of poultry production (Kleyn, 2013) because EP from parent stock and meat production for their progeny are desired traits in the poultry industry. Understanding the dynamics of heat production (HP) and body composition along with EP can provide insights of nutrient utilization but the information is lacking for the modern broiler breeder. Heat production can be measured by indirect calorimetry and by difference between ME intake (MEI) and retained energy (Sakomura, 2004). Body composition can be different at the same body weight (BW) affecting the onset of sexual maturity, so the analysis of lean and fat mass is important (Wilson et al., 1989). Body composition has changed over time resulting in leaner breeders with total protein content being very important at the onset of sexual maturity (De Beer and Coon, 2007). Salas et al. (2012) evaluated the body composition of broiler breeders using dual energy X-ray absorptiometry (DEXA) and reported a decrease in lean mass at 35 and 45 wk of age during production. Vignale et al. (2016) reported that the highest protein degradation rate in pectoralis major breast muscle occurred at 30 to 37 wk of age in broiler breeders. The large increase in degradation rate helps explain the decrease in lean mass at 35 wk reported by Salas et al. (2010). Indirect calorimetry measures volume of oxygen consumption (VO2) and volume of carbon dioxide production (VCO2) to estimate HP. The ratio VCO2/VO2 indicates the nutrient utilization and is called the respiratory exchange ratio (RER). The values for RER are 1.0, 0.74, and 0.70 for carbohydrate, protein, and fat oxidation, respectively, in birds (McLean and Tobin, 1987) and a balanced poultry feed would be a mix of the RER values. Indirect calorimetry can provide data on nutrient oxidation and the DEXA can provide body composition data to understand tissue synthesis and degradation and the dynamics of nutrient utilization in broiler breeder hens. The objectives of the present study are to study the same breeders during production from 26 to 59 wk of age: 1) to evaluate changes in calorimetry parameters with age: VO2, VCO2, RER, and HP, and 2) to determine changes in body composition with age: lean mass, fat mass, and bone mineral content (BMC). MATERIALS AND METHODS All management practices and procedures were approved by the University of Arkansas Institutional Animal Care and Use Committee # 13002. Hens and Housing A total of 12 parent stock females from Cobb 500 fast feathering (Cobb Vantress, Siloam Springs, AR) were selected from a population of 70 hens at 23 wk of age. Hens were selected to represent a normal BW population with an average BW of 2544 g ± 258 SD (10% CV). Hens were transferred from floor pens to breeder wire cages (47 cm high, 30.5 cm wide, 47 cm deep) equipped with an individual feeder and nipple drinker. The photoperiod was 16L: 8D from 26 to 59 wk. The same 12 hens were evaluated in respiratory chambers and with the DEXA 10 different times during production (26, 30, 33, 37, 40, 43, 45, 50, 54, and 59 wk of age). Hens were moved to respiratory chambers for 24 h before each evaluation to acclimate the breeders to the chambers. The hens were only acclimated for 24 h prior to evaluation because the hens were maintained in wire cages with similar dimensions and floor type to the respiratory chambers. The breeder cage also contained a similar drinker and feeder system compared to the respiratory chambers. The acclimation period was adequate because breeder hen behavior, feed consumption time, and EP remained normal performance with the Cobb 500 breeder guide, 2013). Temperature was kept at 21°C through production (Cobb 500, 2008) in cages and respiratory chambers. Egg production was recorded daily and averaged for 12 hens at every week of evaluation. Respiratory Chambers Respiratory chambers were made from polycarbonate plastic glass (61 cm long × 51 cm wide × 56 cm high) and equipped with 1 feeder and 1 nipple drinker according to the specifications of FASS 2010 (Champaign, IL). The environmental condition of the room for the respiratory chambers was the same as the metabolic cages. The room for the metabolic chambers was equipped with 2 heating and air conditioning units. These units were controlled by a Honeywell programmable thermostat that automatically switches between cooling and heating within a 2°C range. Minimum ventilation was provided by 2 ventilation fans that exhaust to the outside and draw fresh air from the hall. Each ventilation fan was controlled by a timer. The on/off cycle was adjusted as needed to maintain room air quality and desired CO2 levels. To control humidity, the room was equipped with 2 de-humidifiers (GE, Madison, WI) that remained running continuously. Relative humidity (RH) was kept at 80% (range 70 to 90%) depending on the RH of the environment. Temperature inside the chamber was 21°C (range 19 to 23°C). The room temperature was 16°C, which is 5°C lower than temperature inside the chambers to ensure the temperature inside the respiratory chambers stayed at 21°C. The indirect calorimetry system provided air flow of 12 to 15 L/min depending on the size of the hen. Delta carbon dioxide, ΔCO2 (CO2 out –CO2 in), was between 0.30 and 0.50. The gas evaluations in each chamber were measured every 12 min making 5 readings per hour and 120 readings in 24 h. The daily gas evaluation was composed of 67% during the light time (3 am to 6 pm) and 33% during the dark time (7 pm to 3 am). Diet and Feed Program Hens were fed a commercial crumbled feed during evaluation (Cobb-Vantress, Siloam Springs, AR). The breeder diet, which was provided from 22 to 58 wk of age, was formulated to have 2920 kcal/kg of ME with 15.5% crude protein. Four batches of diet were received during the 38-wk period and analyzed for proximal analysis on arrival (Table 1). Feed and energy allowance was 123 g (359 kcal/d) at 26 wk and 134 g (390 kcal/d) at 30 wk (peak production). This caloric intake was lower than Cobb's suggested value but it was used to account for the reduced energy expenditure of individually caged hens (Reyes et al., 2011, 2012). The 390-kcal ME peak feed was determined to be the requirement for breeders in cages by Salas et al. (2010). The group was fed the same amount for the 38-wk study to avoid the introduction of additional variables with the feed withdrawal period. Hens were individually fed every day at 7 am in cages and chambers. The feed was cleaned up after approximately 1 h. Fresh water was provided ad libitum during evaluation. Table 1. Composition and nutrient calculations (g/100 g as fed) of the diet. Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 1(HMTBa Met) 2-hydroxy-4-methylthio-butanoic acid. 2Supplied per kilogram of diet: vitamin A, 10,582 IU; vitamin D3, 5291 IU; vitamin E, 53 IU; vitamin B12, 0.024 mg; biotin, 0.26 mg; menadione, 2.65 mg; thiamine, 2.65 mg; riboflavin, 15.9 mg; pantothenic acid, 26.5 mg; pyridoxine, 5.29 mg; niacin, 59.5; folic acid, 2.6 mg, choline chlorine, 1543 mg. 3Supplied per kilogram of diet: Mn,100 mg; Zn, 110 mg; Fe, 48 mg; Cu, 13 mg, I, 2 mg; Se, 0.30 mg. View Large Table 1. Composition and nutrient calculations (g/100 g as fed) of the diet. Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 Ingredient, % Yellow corn (7.2% CP) 65.00 Soybean meal (47.0% CP) 22.81 Poultry fat 3.04 Alimet1 0.24 Calcium carbonate 6.76 Defluorinated phosphate 1.82 Sodium chloride 0.21 Vitamin premix2 0.20 Mineral premix3 0.10 Calculated composition ME, kcal/kg 2920 Crude protein 15.5 Calcium 3.25 Non-phytate phosphorus 0.41 Digestible lysine 0.75 Digestible methionine + cysteine 0.68 Digestible threonine 0.51 Digestible arginine 0.93 Digestible tryptophan 0.16 Analyzed composition AMEn, kcal/kg 2880 Crude protein 16.1 Crude fat 4.9 1(HMTBa Met) 2-hydroxy-4-methylthio-butanoic acid. 2Supplied per kilogram of diet: vitamin A, 10,582 IU; vitamin D3, 5291 IU; vitamin E, 53 IU; vitamin B12, 0.024 mg; biotin, 0.26 mg; menadione, 2.65 mg; thiamine, 2.65 mg; riboflavin, 15.9 mg; pantothenic acid, 26.5 mg; pyridoxine, 5.29 mg; niacin, 59.5; folic acid, 2.6 mg, choline chlorine, 1543 mg. 3Supplied per kilogram of diet: Mn,100 mg; Zn, 110 mg; Fe, 48 mg; Cu, 13 mg, I, 2 mg; Se, 0.30 mg. View Large Body Composition Analysis Hens were scanned the previous day before evaluation in the respiratory chambers using a DEXA scanner (GE) with a small animal body software module (Lunar Prodigy from GE encore version 12.2). Green lights were set up in the DEXA room to help keep the hens calm while scanning for about 3.5 to 4 min per hen. No chemicals or anesthesia was used and hens were scanned at the same time (around 1 pm) at every point of evaluation. Hens were returned to the respiratory chambers after scanning. Total tissue, lean mass, fat mass, and BMC were adjusted to body composition values analyzed by chemical analysis using equations previously developed by Salas et al. (2012). Calculation Data from indirect calorimetry were separated as time of day (light or dark) and averaged within a day. VO2, VCO2, and RER (VCO2/VO2) were calculated as liters per day (L/d) for the development of the mixed model and normalized to metabolic BW (L/kg BW0.75) for comparative purposes. Heat production was obtained using the Brouwer equation: HP kcal/d = 3.866 VO2 L/d + 1.233 VCO2 L/d (MacLean and Tobin, 1987). Heat production was calculated as kcal/d and kcal/kg0.75. The body composition was reported as g and g/kg: lean, fat, and BMC. Tissue gain (g/d) was calculated over the period between 2 proximate ages evaluated. For example, 10.5 g/d of lean tissue was BW 30 wk – BW 26 wk divided by the number of days between these 2 ages, and the same calculations for the next periods (g/d). Statistical Analysis A mixed model was used to evaluate calorimetry parameters: HP (kcal/d), VO2 (L/d), VCO2 (L/d) with age (d), BW (kg), and time of day (2 levels: light and dark) as fixed effects. The breeder hen was considered a random effect being the hens were measured repeatedly at every age. For normalized calorimetry data (kcal/kg BW0.75 and L/kg BW0.75), a 2 × 10 factorial design (time of day × age) was analyzed. The body composition data were analyzed by a complete randomized design utilizing one-way ANOVA (age) with hen as random effect. Means were separated by the Tukey-HSD test. Fat gain (X) was fitted against Lean gain (Y) in a simple linear regression. P-value was considered significant when P ≤ 0.05. All analyses were determined with JMP12 (SAS, 2015). RESULTS Calorimetry Parameters Heat production or heat expenditure is the result of indirect calorimetry evaluation: volume of oxygen consumption (VO2) and carbon dioxide production (VCO2). The HP was measured during the EP cycle of the broiler breeder. A mixed model provided the opportunity to understand the dynamics of VO2, VCO2, and HP by age and time of day (light and dark periods) with repeated measurements such as the case of the present study where the same hen was evaluated at every point of evaluation. Gases and HP were increased as the age increased from 26 to 59 wk: 0.031 L/d VO2, 0.024 L/d VCO2, and 0.15 kcal/d HP (P < 0.01) (Table 2). At the end of the 38-wk study (59 wk of age of the breeder), HP was the highest because of a gain in body tissue that was mainly lean mass gain during the 45- to 59-wk period of the production cycle. Breeder hens consumed +17.4 L/d more oxygen, produced +18.9 L/d more carbon dioxide, and produced + 89.8 kcal/d more heat during the light period (3 am to 6 pm) compared to the dark period (7 pm to 2 am) during the 38-wk study. The increase in HP during the light time is because of higher activity and metabolic processes that occur during this time. The VO2, VCO2, and HP parameter estimates of the mixed model provide half of this difference (8.7 VO2/d, 9.4 VCO2/d, and 44.9 kcal/d), respectively (Table 2), due to 2 periods being evaluated (light and dark). VO2 was always higher than VCO2 in the light and dark periods (Table 3). The interaction effect of time of day and age was not significant (P > 0.05) when VO2, VCO2, and HP were expressed based on BW (L/kg BW0.75 and kcal/kg BW0.75) (Table 3). The breeder hens based on their metabolic BW consumed 27% more VO2 (6.1 L/kg BW0.75), produced 30% more VCO2 (6.5 L/kg BW 0.75), and 27% more HP (31 kcal/kg BW0.75) (P < 0.01) during the light period compared to the dark period. The RER was also higher during the light period (0.955 vs. 0.907) (P < 0.01) compared to the dark period meaning there are differences in nutrient utilization between light and dark periods (Table 3, Figure 1). At the end of the 38-wk production period, 59-wk-old hens had increased oxygen consumption (L/kg BW0.75) compared to <50-wk-old hens with exception of 30-wk-old hens during peak production (P < 0.01). The VCO2 production (L/kg BW0.75) was the highest at 59 wk compared to younger ages other than 26, 30, and 37 wk of age (P < 0.01). Heat production (kcal/kg BW0.75) was significantly increased with 59-wk-old hens (106 kcal/kg BW0.75) compared to previous younger ages, except for breeder hens at 30 wk of age. Breeder hens at 30 wk of age had higher VO2 consumption and VCO2 production because the breeders were at peak EP. Respiratory exchange ratio was the lowest at 43 wk of age (P < 0.01) compared to other ages, except breeders 40 and 50 wk of age. The highest RER was found at 30 wk compared to other ages except 26 wk (P < 0.01). Figure 1. View largeDownload slide Respiratory exchange ratio (RER) during daily light and dark time period for 26- through 59-wk-old broiler breeders. Factorial design 2 × 10 (time of day × age). Levels (a, b, c, d) not connected by same letter are significantly different between ages for both light and dark period, Tukey-HSD test P < 0.05. P-values: time of day P < 0.01, age P < 0.01, Time of day × age = 0.673. Figure 1. View largeDownload slide Respiratory exchange ratio (RER) during daily light and dark time period for 26- through 59-wk-old broiler breeders. Factorial design 2 × 10 (time of day × age). Levels (a, b, c, d) not connected by same letter are significantly different between ages for both light and dark period, Tukey-HSD test P < 0.05. P-values: time of day P < 0.01, age P < 0.01, Time of day × age = 0.673. Table 2. Mixed model for volume of oxygen consumption (VO2), carbon dioxide production (VCO2), and heat production (HP) for broiler breeders from 26 to 59 wk of age. Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 View Large Table 2. Mixed model for volume of oxygen consumption (VO2), carbon dioxide production (VCO2), and heat production (HP) for broiler breeders from 26 to 59 wk of age. Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 Y = VO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VO2 (L/d) = 24.27 + 0.031 × Age (d) + 5.85 × BW (kg) + match time of day [if light 8.7; if dark –8.7] 1309 Intercept 24.27 4.08 16.08 32.44 Age (d) 0.031 0.009 0.01 0.05 BW (kg) 5.85 0.98 3.46 8.24 Time of day (light) 8.70 0.22 8.26 9.13 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 15.0 6.7 1.96 28.06 Cov (Age, Intercept) 0.0047 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 11.29 1.09 9.42 13.80 Y = VCO2 (L/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% VCO2 (L/d) = 26.80+ 0.024 ×Age (d) + 4.76 × BW (kg) + match time of day [if light 9.44; if dark –9.44] 1347 Intercept 26.80 5.19 18.30 35.36 Age (d) 0.024 0.027 0.004 0.04 BW (kg) 4.76 0.0003 2.17 7.34 Time of day (light) 9.44 1.33 8.96 9.91 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 11.4 6.7 1.96 28.06 Cov (Age, Intercept) 0.0001 0.0310 –0.056 0.066 Var (Age) 0.0005 0.0003 –0.00003 0.001 Residual 13.72 1.33 11.44 16.76 Y = Heat (Kcal/d) –2 log likelihood Fixed effects Estimate Std error Lower 95% Upper 95% Heat (Kcal/d) = 127.9+ 0.152 ×Age (d) + 27.54 × BW (kg) + match time of day [if light 44.92; if dark –44.92] 2080 Intercept 127.90 20.63 86.56 169.20 Age (day) 0.152 0.047 0.050 0.25 BW (kg) 27.54 6.1300 15.45 39.64 Time of day (light) 44.92 1.11 42.74 47.10 Random effects (Hen) Estimate Std error 95% Lower 95% Upper Var (Intercept) 353.8 157.7 44.71 662.91 Cov (Age, Intercept) 0.07 0.77 –0.056 1.589 Var (Age) 0.014 0.01 –0.00003 0.028 Residual 289.90 28.17 11.44 354.17 View Large Table 3. Calorimetry parameters VO2 L/kg0.75, VCO2 L/kg0.75, and HP kcal/kg0.75 for broiler breeders from 26 to 59 wk of age. 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 Levels (a, b, c, d) not connected by same letter within the columns are significantly different. 1VO2 = volume of oxygen consumption L/kg0.75/d. 2VCO2 = volume of carbon dioxide production L/kg0.75/d. 3HP = heat production kcal/kg0.75/d. 4RER = respiratory exchange ratio. 5SEM = standard error mean. View Large Table 3. Calorimetry parameters VO2 L/kg0.75, VCO2 L/kg0.75, and HP kcal/kg0.75 for broiler breeders from 26 to 59 wk of age. 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 1VO2 L/ 2VCO2 L/ 3HP kcal/ 4RER Time of day kg0.75/d kg0.75/d kg0.75/d (VCO2/VO2) Light 23.0 21.9 115 0.955 Dark 16.9 15.4 84 0.907 Dif. units 6.1 6.5 31 0.048 Dif. % +27 +30 +27 +5 5SEM 0.37 0.37 1.82 0.006 Age 26 19.8b 19.0a,b 100b,c 0.952a,b 30 20.4a,b 19.8a 103a,b 0.966a 33 19.8b 18.5b,c 99b,c 0.931b,c 37 19.9b 18.7a,b,c 99b,c 0.934b,c 40 19.8b 18.2b,c 98b,c 0.919c,d 43 19.8b 18.0b,c 98b,c 0.903d 45 19.2b 17.8c 96c 0.924c 50 19.4b 17.8c 96c 0.914c,d 54 20.1a,b 18.9a,b 101a,b,c 0.934b,c 59 21.2a 19.8a 106a 0.933b,c SEM 0.42 0.39 2.2 0.008 P-value Time of day <0.01 <0.01 <0.01 <0.01 Age <0.01 <0.01 <0.01 <0.01 Time of day × age 0.912 0.850 0.927 0.673 Levels (a, b, c, d) not connected by same letter within the columns are significantly different. 1VO2 = volume of oxygen consumption L/kg0.75/d. 2VCO2 = volume of carbon dioxide production L/kg0.75/d. 3HP = heat production kcal/kg0.75/d. 4RER = respiratory exchange ratio. 5SEM = standard error mean. View Large Body Composition For body composition evaluation, a CRD design provides differences in tissue composition between ages (Table 4). Total mass that is equivalent to scale BW was higher at 50, 54, and 59 wk compared to 26, 30, 33, 37, and 40 wk (P < 0.01). Lean mass was the highest at 59 wk (3031 g) compared to 26, 37, and 50 wk (P < 0.01). The lowest lean mass was found at the beginning of production at 26 wk of age compared to 33, 40, 43, 54, and 59 wk. The absolute lean mass for breeder hens at 37, 45, and 50 wk was not different from the 26-wk-old hen (P < 0.01). Fat mass was the highest at 50 wk compared to other ages except 54 wk. The smallest amount of fat was found to be at the beginning of production (26 wk) compared to hens older than 37 wk (P < 0.01). The BMC reached the highest point at 50 wk (187 g) compared to other ages except 37, 45, 54, and 59 wk (P < 0.01). The smallest amount of BMC was at 30 wk compared to 50 wk. Body composition expressed as g/kg provides meaningful information about the relative body composition between ages (Figure 2). Lean mass (g/kg) was the highest at 26, 30, 33, and 40 wk of age and the lowest at 50 wk compared to other ages except 45 and 54 wk of age. Lean mass (g/kg) shows the first low point at 37 wk compared to the initial body composition (26 wk), and the second lowest point at 50 wk. Lean mass tends to decrease from peak until 50 wk and then increase after 50 wk. Fat mass (g/kg) was the lowest at the beginning of production and it increased gradually becoming significant after 43 wk. The largest amount of fat (g/kg) was found at 45, 50, and 54 wk (P < 0.01). Fat composition tends to increase with age reaching the highest point at 50 wk but drops after and being significantly lower at for 59 wk old, end of the present study (Figure 2). The BMC (g/kg) was higher at 50 wk compared to 33 and 40 wk (P < 0.01). Lean gain (g/d) was variable during the EP cycle and the values ranged from –6.5 g/d during 30 to 37 wk to +10.4 g/d during 26 to 30 wk. Lean gain at 37 wk was significantly lower compared to 30 and 40 wk hens (P < 0.01) suggesting protein tissue being oxidized during this period. Lean tissue was also negative at 50 wk compared to 30 and 40 wk (P < 0.01). Fat gain (g/d) was the highest at 37 and 50 wk compared to 40, 54, and 59 wk (P < 0.01). Figure 3 depicts the linear relationship between fat tissue gain and protein tissue gain. For every daily gram of lean gain, fat gain decreased 0.45 g/d during 26 to 59 wk old. Figure 2. View largeDownload slide Lean and fat body mass g/kg of broiler breeders from 26 to 59 wk of age. Graph above: body lean mass g/kg. Graph below: body fat mass g/kg. Levels (a, b, c, d, e, f) not connected by same letter are significantly different, Tukey-HSD test P < 0.05. Figure 2. View largeDownload slide Lean and fat body mass g/kg of broiler breeders from 26 to 59 wk of age. Graph above: body lean mass g/kg. Graph below: body fat mass g/kg. Levels (a, b, c, d, e, f) not connected by same letter are significantly different, Tukey-HSD test P < 0.05. Figure 3. View largeDownload slide Linear regression between fat tissue gain g/d vs. lean tissue gain g/d. Fat gain g/d = 2.811 – 0.45 × lean gain g/d; intercept P < 0.01; slope P < 0.01; R2 = 0.68; RMSE = 3.6. Figure 3. View largeDownload slide Linear regression between fat tissue gain g/d vs. lean tissue gain g/d. Fat gain g/d = 2.811 – 0.45 × lean gain g/d; intercept P < 0.01; slope P < 0.01; R2 = 0.68; RMSE = 3.6. Table 4. Body composition and tissue gain for broiler breeders from 26 to 59 wk of age. Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Levels (a, b, c, d, e, f) not connected by same letter within columns are significantly different. 1Total mass = body weight. 2BMC = bone mineral content. 3SEM = standard error mean. View Large Table 4. Body composition and tissue gain for broiler breeders from 26 to 59 wk of age. Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Age, wk 1Total mass, g Lean mass, g Fat mass, g 2BMC, g Lean mass, g/kg Fat mass, g/kg BMC, g/kg Lean gain g/d Fat gain g/d 26 3335e 2611c 563f 131b 783a 169f 39a,b 30 3701d 2857a,b,c 655e,f 130b 771a,b 177e,f 35a,b 10.4a 3.8a,b 33 3878c,d 2942a,b 721d,e,f 132b 758a,b,c 186d,e,f 34b –0.4b,c 3.6a,b,c 37 3844c,d 2719b,c 868c,d 160a,b 702c,d,e 224b,c,d 41a,b –6.5b 5.2a 40 4015b,c 2933a,b 820c,d,e 132b 732a,b,c,d 203c,d,e,f 33b 10.3a −2.2c 43 4132a,b,c 2966a,b 880b,c,d 150b 719b,c,d,e 212b,c,d,e 36a,b 3.5a,b 0.7a,b,c 45 4161a,b 2831a,b,c 988a,b,c 162a,b 681d,e,f 237a,b,c 39a,b 2.1a,b 2.8a,b,c 50 4336a 2745b,c 1158a 187a 634f 267a 43a –2.6b 5.2a 54 4386a 2939a,b 1065a,b 165a,b 671e,f 242a,b 38a,b 2.7a,b –0.7b,c 59 4297a 3031a 945b,c 155a,b 708c,d,e 218b,c,d 36a,b 1.2a,b –1.6b,c SEM3 70.4 70.8 50.7 9.7 15.4 10.2 1.7 2.3 1.3 P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Levels (a, b, c, d, e, f) not connected by same letter within columns are significantly different. 1Total mass = body weight. 2BMC = bone mineral content. 3SEM = standard error mean. View Large DISCUSSION Calorimetry Parameters and EP The amount of VO2 and VCO2 for modern broiler breeders is rarely reported. Past research with meat-type breeders reports 14.6 L/kg BW0.75 for oxygen consumption (Waring and Brown, 1965), which is lower than the 20 L/kg BW0.75 value reported in the present experiment. This may be due to modern breeders having more lean tissue than breeders in 1965 when compared on a metabolic BW basis (L/kg BW0.75). The increase in VO2 in broiler breeders in the present study represents a 37% increase in oxygen consumption compared to breeder VO2 from 1965 accounting for an increase of 0.74 L/kg BW0.75 of oxygen per year. It is well known that breast yield is higher in progeny from modern high-yielding broiler breeders and the progeny genetic potential for increased lean mass is higher than before (Havenstein et al., 2003). When compared to broilers, broiler breeders have a lower VO2 and VCO2 (L/kg BW0.75) (Fedde et al., 1998). This author reported 42 L/kg BW0.75 VO2 and 40 L/kg BW0.75 VCO2 in broilers with 1.38 kg BW at 35 d, which is almost twice the amount of VO2 and VCO2 found in breeders (20 L/kg BW0.75). The increased quantitative amount of gases for broilers reported by Fedde et al. (1998) agrees with data reported by Caldas et al. (2016). The reason there is an increased oxygen consumption and carbon dioxide production in modern broilers compared to broiler breeders is because of the high growth rate and ad libitum feed consumption for broilers while breeder hens are fed restricted amounts of feed during EP to avoid over weight hens. Heat production is considered to be a measure of energy use for maintenance, activity, and heat increment. Metabolizable energy for maintenance (MEm) was evaluated during fasting period, so no activity and no heat increment of feeding were included in the measurement. Maintenance energy is the highest proportion of ME needed by the modern breeder hen accounting for 79% of the energy intake at peak EP at normal temperature, 21°C (Reyes et al., 2011). The MEm has been reported to be 88 kcal/kg0.75/d Hubbard meat type in broiler breeders (Spratt et al., 1990a,b) and 98.3 kcal/kg0.75/d with Cobb500 genetics at 21°C (Reyes et al., 2011, 2012). There is little research that reports HP values per se from broiler breeders using calorimetry systems, so comparisons become complicated. In the present experiment, HP has been measured during light and dark times and resulted in 115 and 84 kcal/kg0.75/d, respectively. The HP in the dark period is similar to the MEm reported by previous authors, because the HP in the dark period does not account for activity and heat increment because hens were fed 12 h earlier. Determining the difference of 31 kcal/kg0.75/d between the light and dark period is the energy of activity and heat increment during the light period. The determination of MEm was not the main focus of this study but HP accounts for a high percentage of maintenance. The highest HP of 106 kcal/kg0.75/d was at 59 wk of age (end of the study) compared to 100 kcal/kg0.75/d at the beginning of lay, 26 wk. The increased HP caused by an increase in lean mass in the 59-wk breeder while fat tissue was decreasing suggests the hen is using fat calories to maintain the higher BW achieved at the end of the experiment. Protein synthesis produces more HP due to protein using more oxygen than fat synthesis (Teeter et al., 1996). This author showed that the oxygen required per unit protein synthesized was 380% greater than for fat. Another measurement that provides energy utilization is RER. It provides means to differentiate nutrient utilization between carbohydrates, protein, and fat because these are the only nutrients assumed to release energy for maintenance of life in the human and animals (McLean and Tobin, 1987). The RER for the oxidation of carbohydrates, protein, and fat in chickens is 1.0, 0.74, and 0.70, respectively (MacLean and Tobin, 1987). Because the breeder diet is a balance of carbohydrates, proteins, and fats, the RER data can only be compared between ages. RER reached the lowest point at 40 to 43 wk of age that could mean more fat and/or protein oxidation is occurring at that time compared to carbohydrate utilization at the beginning of production. The breeder RER decreases at 45 wk and remains low suggesting the hens were using less carbohydrates at 45 wk compared to 30 wk at peak production. Salas et al. (2017) used stable isotopes and reported broiler breeder utilized glucose for egg lipid formation at the beginning of production and mobilized dietary fat for egg lipid synthesis at the end of production. Salas and group findings are in partial agreement with the results in the present experiment. High RER variability was seen during egg oviposition times and during day time but the RER data were less variable during the night when activity was decreased. The observed RER differences between hens during the light period may require a different mechanistic model to explain breeder hen's behavior during EP. Additional RER data for breeders in production are needed to help understand the significance of this value and to determine if RER may change with feeding strategies, individual bird variation, and genetics. Body Composition, and EP Lean tissue mass (g and g/kg BW) reached the lowest point at 37 and 50 wk that is in full agreement with the data found by Salas et al. (2010) and Vignale et al. (2016). Vignale and group used 15N phenylalanine to calculate the fractional protein synthesis and degradation rate and found the highest protein degradation rate for pectoralis major was at peak production (30 to 37 wk). The authors suggested the hen utilized breast protein turnover to support EP. These results are in agreement with the negative lean tissue gain found at 37 wk in the present study but the negative tissue lean gain was different only compared to 30 and 43 wk of age breeders and not to other ages because of high variability between hens. After 50 wk of age, EP is decreasing and the hen starts increasing lean tissue. Breeder hens older than 50 wk breeder may be preparing body composition for the next clutch or production cycle as it happens in nature. Lean mass was high at the beginning of production (24 wk) that matches with high fractional protein synthesis rate prior to sexual maturity shown by Vignale et al. (2016). Van Emous et al. (2015) reported breast muscle amount of 17.24% at 35 wk compared to 20.15% at 22 wk and 16.43% at 59 wk. These findings are in partial agreement with the present study. Van Emous and group reported less breast muscle at 35 wk similar to the present study but did not observe an increase in lean mass at 59 wk as found it here. The authors also observed different pattern for fat deposition in their breeder hens compared to present study. The authors suggested abdominal fat increased with age and was the highest at termination of the production period. The authors used a different modern genetic line than the Cobb 500FF as used in the present study that may be the cause of the disagreement. Fat utilization is important in egg lipid formation (Boonsinchai et al., 2016), and a balance of protein and fat utilization exists during the complex EP process. In the present study, fat mass increased with age until 50 wk of age and then body fat mass and % fat declined through 59 wk (termination of study). Body fat utilization for the purpose of supporting EP may not be as important as lean tissue utilization because lean mass decreases when the hen is at peak EP. This is in contrast to fat accumulation that occurs throughout peak production and reaches the highest fat mass and percent fat at 50 wk of age. After 50 wk of age, fat mass and % fat decrease to support the additional maintenance calorie needs of breeders that gain lean mass during the last 1/3 of the production period. The dynamic pattern of breeder fat mass and lean mass change with age observed in present study matches very closely to previous reports by Salas et al. (2010) and Vignale et al. (2016). Bone mineral content is the lowest at peak production (30 wk) compared to 50 wk. Because Ca and P account for 23% and 20% of the BMC, respectively (Caldas, 2015), data suggest high utilization of minerals for egg shell formation during peak production. After 50 wk of age, broiler breeder EP is reduced to less than 50% thus allowing minerals and BMC to increase. Egg production in this experiment was close to the standard (Cobb, 2013). Heat production and body composition change with age but the change along EP is more important because the objective of meat-type breeders is to produce chicks of high quality by producing good quality eggs. Both EP and HP start low at the beginning of the EP (26 wk); peak production was reached at 30 wk and gradually decreased until the end of production (59 wk). Heat production is an inefficient process in terms of EP because it is mostly used for maintenance energy requirement (Chwalibog and Thorbek, 1992; Reyes et al., 2011). Lean mass and EP both increase when going from first egg to peak production, but at peak of production lean tissue tends to drop and EP gradually declines. When lean mass increases after 50 wk of age, EP keeps dropping. Respiratory exchange ratio tends to decrease as EP decreases until 43 wk of age, then RER increases when EP drops after 43 wk. In summary, indirect calorimetry and DEXA can be utilized as tools to better understand why breeders use specific fuel from feed nutrients and body tissue to develop better feeding strategies for feeding the pullet and breeder for maximum production of quality chicks. Acknowledgements The authors acknowledge Cobb-Vantress, Inc. for donating the hens and feed for the present study. REFERENCES Boonsinchai N. K. H. , Mullenix G. , Caldas J. V. , England J. A. , Coon C. N. . 2016 . De novo lipogenesis in broiler breeder hens . 187 – 189 in 5th EAAP Publication 137 . Skomial J. , Lapierre H. , eds. Wageningen Academic Publishers , Krakow, Poland . Caldas J. V. 2015 . Calorimetry and body composition research in broilers, and broiler breeders . PhD Diss. Univ. Arkansas, AR, USA . Caldas J. V. , Hilton K. , Boonsinchai N. , Schlumbohm M. , England J. A. , Coon C. N. , 2016 . 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Poultry ScienceOxford University Press

Published: Jul 11, 2018

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