Effects of environmental temperature and dietary energy on energy partitioning coefficients of female broiler breeders

With increasing disparity between broiler breeder target weights and broiler growth potential, maintenance energy requirements have become a larger proportion of total broiler breeder energy intake. Because energy is partitioned to growth and egg production at a lower priority than maintenance, accurate prediction of maintenance energy requirements is important for practical broiler breeder feed allocation decisions. Environmental temperature affects the maintenance energy requirement by changing rate of heat loss to the environment. In the ME system, heat production (energy lost) is part of the maintenance requirement (MEm). In the current study, a nonlinear mixed model was derived to predict ME partitioning of broiler breeder hens under varied temperature conditions. At 21 wk of age, 192 Ross 708 hens were individually caged within 6 controlled environmental chambers. From 25 to 41 wk, 4 temperature treatments (15 degrees C, 19 degrees C, 23 degrees C, and 27 degrees C) were randomly assigned to the chambers for 2-week periods. Half of the birds in each chamber were fed a high-energy (HE; 2,912 kcal/kg) diet, and half were fed a low-energy (LE; 2,790 kcal/kg) diet. The nonlinear mixed regression model included a normally distributed random term representing individual hen maintenance, a quadratic response to environmental temperature, and linear ADG and egg mass (EM) coefficients. The model assumed that energy requirements for BW gain and egg production were not influenced by environmental temperature because hens were homeothermic, and the cellular processes for associated biochemical processes occurred within a controlled narrow core body temperature range. Residual feed intake (RFI) and residual MEm (RMEm) were used to estimate efficiency. A quadratic effect of environmental temperature on broiler breeder MEm was predicted (P < 0.0001), with a minimum energy expenditure at 24.3 degrees C. Predicted MEm at 21 degrees C was 92.5 kcal/kg(0.84); requirements for gain and EM were 2.126 and 1.789 kcal/g, respectively (P < 0.0001). Birds fed the HE diet were more efficient, with a lower RMEm than birds on the LE diet (-0.63 vs. 0.63 kcal/kg(0.84)), translating to MEm of 135.2 and 136.5 kcal/kg(0.84), respectively. In the current experiment, optimal biological efficiency was predicted at 24.3 degrees C in feed-restricted broiler breeders fed the HE diet.