The branched-chain amino acids (BCAA) leucine, isoleucine, and valine are essential AA needed for energy production, protein synthesis, and anabolic signaling functions via the mammalian target of rapamycin (mTOR) pathway. Imbalanced BCAA ratios can lead to antagonism and degradation of limiting BCAA, particularly in diets with excess leucine. Concentrated corn proteins contain high levels of Leu and can alter BCAA requirement; however, L-Ile and L-Val may be added to balance BCAA ratios. This study evaluated the effects of dietary BCAA ratio using corn gluten meal, L-Ile, and L-Val on performance, mTOR activation, and AA digestibility in commercial turkey hens from 0-21d of age. A 38.4% corn and 49.8% soybean-meal diet was used as the Control. In uncorrected high Leu treatments, feed intake, bird weight, and live weight gain decreased, and feed conversion ratio (FCR) increased relative to the Control at day 14 and 21 (P<0.05). Performance equivalent to the Control was produced with additions of both L-Ile and L-Val at d 14 (P<0.05), and FCR decreased relative to the Control at d 21 (P<0.05). Relative mTOR activation was numerically raised in high Leu diets compared to the control (P=0.13). BCAA digestibility was maximized in high leucine diets with additional L-Ile and L-Val (P<0.05). These results demonstrate that diets containing high Leu from concentrated corn proteins can decrease poult performance, but may be restored with concomitant additions of L-Ile and L-Val. In practical settings, nutritionists should assess the costs associated with BCAA supplementation versus corn and soybean meal-based diets.

This work confirmed that turkey nutritionists need to be careful when adding corn proteins to substitute for soybean meal in turkey diets because corn proteins alter the branched chain amino acids ratios and cause performance problems. Problems were identified with the use of high inclusions of concentrated corn protein i.e. corn gluten meal in commercial turkey starter diets. These problems included live performance, amino acid digestibility, and over activation of the mammalian target of rapamycin (mtor) pathway in modern commercial turkeys. The problems associated with live poult performance, amino acid digestibility, and mtor activation can be remedied with supplementation of branch chain amino acids L-Ile and L-Val to mimic ratios achieved in corn and soybean meal diets. The control diet that contained 49.8% soybean meal and 38.4% corn produced the numerically highest D0-21d poult hen feed intake and live weight gain equivalent to the concentrated corn protein diet with added L-Ile and L-Val. In practical settings, nutritionists should assess the costs associated with BCAA supplementation versus corn and soybean meal-based diets.