Performance and meat production of broiler chickens fed diets formulated at different crude protein levels supplemented or not with L-valine and L-isoleucine

• Broilers were fed diets formulated using approaches routinely used by the industry to the third limiting amino acid only (Thr).
• Supplementation was done also with L-Valine and L-Isoleucine.
• Broilers fed supplemental L-Valine and L-Isoleucine had competitive performance and carcass yield results as compared to those fed higher CP diets not supplemented with these AA.

A total of 4,800 one day (d) old Cobb 500 male broilers was used in a study with the objective of evaluating dietary programs formulated with different degrees of restriction in crude protein (CP) and the supplementation of L-valine and L-isoleucine. Four feeding programs (PRG) reflecting different strategies to deliver amino acids (AA) to broilers were used, respectively from d 1 to 7, 8 to 21, 22 to 35 and 36 to 42, as follow: PRG 1, CP restricted to 224, 211, 198 and 184 g/kg with minimum digestible AA to lysine (Lys) ratios only set for total sulfur AA (TSAA) (0.72) and threonine (Thr) (0.65); PRG 2, as PRG 1 without CP restriction with AA ratios to Lys extended to valine (Val) (0.77) and isoleucine (Ile) (0.67); PRG 3, as PRG 2 supplemented with L-Val and PRG 4, as PRG 3 supplemented with L-Ile. Replications of the 4 PRG provided from 1 to 21 d were further divided into the 4 respective PRG given from 22 to 42 d for total of 16 treatments. The study was conducted as a completely randomized block design with 2 time blocks and 24 replications per treatment per block from 1 to 21 d and 12 replications from 22 to 42 d. Overall, there were no effects for time block or interaction between PRG fed from 1 to 21 and 22 to 42 d of age. Performance and processing data demonstrated benefits of formulating diets using minimum ratios of Val and Ile. Body weight gain was higher when both AA were supplemented together (PRG 4). On the other hand, feed conversion ratio (FCR) was improved when the ratios Val and Ile to Lys were obtained without the use of synthetic sources. Carcass yield data was not affected by PRG with the exception of the proportion of abdominal fat that was reduced (P<0.05) when broilers were fed diets with minimum ratios of Val and Ile without using synthetic sources. In conclusion, formulation of diets for broilers without minimum CP level but using AA to Lys ratios as in PRG 2, 3 and 4, allowed competitive growth performance and carcass yield results. Using L-Val and L-Ile led to improved FCR and, therefore, this possibility should be explored to maintain the efficiency of broiler meat production.