Metabolism and Nutrition V: Energy and Enzymes

Feed ingredient costs have been a concern to the U.S. broiler industry. Some integrated operations have reduced apparent metabolizable energy (AMEn ) values to decrease live production costs. Our laboratory has previously determined that 36 to 47 d feed conversion and caloric conversion were optimized with broilers fed diets formulated at 3,200 kcal/ kg. Finishing broilers may respond to diets formulated to AMEn higher than 3,200 kcal/kg during a summer grow-out. This research evaluated performance and meat yield of broilers fed diets varying in AMEn. Ross × Ross 708 chicks were randomly distributed into 96 floor pens (48 pens of males and females, respectively) at 1 d of age and were fed a common starter and grower diets until 35 d of age. At 36 d of age, all pens were equalized with 15 birds (0.09 m2/bird) and fed the experimental diets until 47 d of age. Six dietary treatments ranging in AMEn from 3,140 to 3,240 kcal/kg in increments of 20 kcal/kg were fed to male and female broilers. During experimentation, ambient temperature set point was 25 °C. Broilers fed gradient additions of AMEn had linear increases (P ≤ 0.03) in BW, BW gain, carcass weight, total breast meat weight, and plasma free fatty acids. Increasing AMEn decreased (P ≤ 0.02) 36 to 47 d feed conversion and caloric conversion linearly. Optimum AMEn approximated 3,240 kcal/kg from 36 to 47 d of age based on BW gain, feed conversion, caloric conversion, and total breast meat weight. Linear AMEn × gender interactions (P≤0.05) were observed for BW, BW gain, feed conversion, caloric conversion, carcass weight, total breast meat weight, and plasma T3. These results indicated that male and female broilers from 36 to 47 d of age subjected to moderate temperatures responded to higher AMEn than previous research with 36 to 47 d old broilers reared under thermoneutral conditions.