Tryptophan and the branched-chain amino acids (BCAA) leucine, isoleucine, and valine are essential amino acids (AA) for poultry. Larger inclusions of concentrated corn proteins can increase Leu levels above requirement, leading to metabolic antagonism and degradation of limiting BCAA in the diet. Excess Leu may also inhibit Trp absorption, transport, and thus, serotonin synthesis. Hence, high-Leu diets could be corrected with supplementary L- Val, L-Ile, and L-Trp to prevent performance reductions associated with imbalanced BCAA/Trp ratios. This study evaluated the effects of varying dietary BCAA/Trp ratios using corn gluten meal, L-Val, L-Ile, and L-Trp on performance, plasma serotonin concentration, immune organ weight, and tibia mineralization in commercial turkey hens from 0-28d of age. A 34.8% corn and 54.0% soybean meal diet served as the Control. Diets were fed to 15 replicate cages of poults utilizing a randomized complete block design. Performance, tibia, and immune organ data were analyzed using a one-way ANOVA followed by Fisher’s LSD (α=0.05). Plasma serotonin data was calculated using a 4PL regression and analyzed using a one-way ANOVA followed by Tukey’s HSD test. Uncorrected high-Leu diets (1.6 Leu:Lys) reduced FI, BW, and LWG relative to the Control at d14 (P<0.05). Fully corrected high- Leu diets with additions of L-Val, L-Ile, and L-Trp produced equivalent FI and increased BW and LWG relative to the Control at d14, 21, and 28 (P<0.05). Plasma serotonin concentrations were lower in the uncorrected high-Leu diet and Ile-corrected high-Leu diet than the Control (P<0.05). Spleen weight was lower in poults fed the fully corrected high-Leu diets than the Control diet (P<0.05), and tibia ash mg/chick was highest in the fully-corrected diet compared to both the Control and high-Leu diets (P<0.05). These results suggest that performance reductions from excess Leu may be most important at d14, although high-Leu diets with corrective inclusions of L-Val, L-Ile, and L-Trp can restore or enhance performance throughout a 28d starter phase in turkeys. However, nutritionists should consider the cost of corn and soybean meal-based diets with higher inclusion levels of feed- grade AA and concentrated corn proteins.

Estanich, E.,  K. Bowen, L. Knarr, E. Lynch, S. Noll, A. Garcia- Morales and J. Moritz. 2025. Varying branched-chain amino acid and tryptophan ratios in corn and soybean meal-based diets influences 0-28d turkey poult performance, blood plasma serotonin concentration, relative immune organ weight, and tibia mineralization. 2025 International Poultry Scientific Forum, Abstract M141.