Response of growing chicks to supplementation of low protein diets with leucine, valine and glycine-glutamic acid

This experiment was conducted to determine the interaction effects that resulted from supplementation of low-protein diets with leucine (Leu), valine (Val), and glycine-glutamic acid (Gly-Glu) on growing broiler chicks from 11 to 24 days old. Two levels of digestible Leu (1.07 and 1.50%) and three levels of digestible Val (0.64, 0.74, and 0.84%) were investigated as a 2 × 3 factorial arrangement of treatments with 12 replicates. The diet with 1.07% digestible Leu and 0.84% digestible Val was supplemented with 0.34% Gly and 1.32% Glu as an additional treatment (T7). At 24 days old, 0.84% Val significantly improved feed conversion with 1.07% Leu, but 0.74% Val was sufficient with 1.50% Leu. The T7 diet further improved feed conversion. Increasing dietary Val from 0.64% to 0.74% significantly increased bone density and strength at the lower level of dietary Leu, while T7 significantly increased tibia breaking strength. There were significant Leu × Val interactions for villus height, crypt depth, and goblet cell numbers. Val at 0.84% maximized the development of the jejunum at the lower Leu level, while goblet cell number and crypt depth were impaired by increments of Val at the higher level of Leu. In conclusion, increasing the level of Val in low-protein grower diets significantly improved performance, bone and jejunum development of broilers, and its interaction with Leu was important. Therefore, these two amino acids (AAs) and the possibility of Gly-Glu fortification must be considered when formulating low-protein broiler diets. Keywords: bone traits, branched-chain amino acids, broilers, gut histology, performance