Balanced corrections of branched-chain amino acids and tryptophan in corn and soybean meal-based turkey starter diets with excess leucine restores d14 performance and d28 blood plasma serotonin concentration and enhances d28 performance and tibia mineralization

Large inclusions of concentrated corn proteins in commercial poultry diets can increase leucine levels above requirement, leading to antagonisms among limiting branched-chain amino acids (BCAA). Excess leucine may also inhibit tryptophan metabolism. High-leucine diets can be corrected with crystalline amino acids to prevent imbalanced BCAA/tryptophan ratios. This study evaluated the effects of varying dietary BCAA/tryptophan ratios using corn gluten meal, L-valine, L-isoleucine, and L-tryptophan on performance, plasma serotonin concentration, immune organ weight, and tibia mineralization in turkey poults from 0-28 days. A corn and soybean meal-based diet served as the Control. Uncorrected, high-leucine diets (1.6 leucine:lysine) reduced feed intake (FI), bird weight (BW), and live weight gain (LWG) relative to the Control at d14 (P<0.05). Fully-corrected high-leucine diets with additions of L-valine, L-isoleucine, and L-tryptophan produced equivalent FI and increased BW and LWG relative to the Control at d14, 21, and 28 (P<0.05). Serotonin concentrations were lower in the uncorrected, high-leucine diet and isoleucine-corrected diet than the Control (P<0.05). Spleen weight was lower and tibia ash was higher in poults fed the fully-corrected high-leucine diets than the Control (P<0.05). These results suggest that performance reductions from excess leucine may be most significant at d14, although high-leucine diets with corrections of L-valine, L-isoleucine, and L-tryptophan can maintain or enhance performance compared to a corn-soy control throughout a 28d starter phase in turkeys. Nutritionists should consider the economic and performance costs associated with higher inclusion levels of these feed-grade amino acids and concentrated corn proteins.