Additional isoleucine without valine in an imbalanced branched-chain amino acid diet further exacerbates its negative effects in broilers

Authors: GOO, DOYUN - University Of Georgia; CHOI, JANGHAN - Orise Fellow; LEE, JIHWAN - University Of Georgia; SHARMA, MILAN - University Of Georgia; PANERU, DEEPENDRA - University Of Georgia; RAFIEIAN-NAEINI, HAMID - University Of Georgia; Zhuang, Hong; Kong, Byungwhi; Bowker, Brian; RITZ, CASEY - University Of Georgia; KIM, WOO - University Of Georgia

Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2025
Publication Date: 10/28/2025
Citation: Goo, D., Choi, J., Lee, J., Sharma, M.K., Paneru, D., Rafieian-Naeini, H.R., Zhuang, H., Kong, B.C., Bowker, B.C., Ritz, C.W., Kim, W.K. 2025. Additional isoleucine without valine in an imbalanced branched-chain amino acid diet further exacerbates its negative effects in broilers. Journal of Applied Poultry Research. 34(4). https://doi.org/10.1016/j.japr.2025.100631.
DOI: https://doi.org/10.1016/j.japr.2025.100631

Interpretive Summary: Branched-chain amino acids (BCAAs) refer to three essential amino acids, leucine, valine, and isoleucine, which cannot be synthesized by animals and must come from the diet. The BCAAs not only serve as building blocks for proteins but also regulate protein synthesis and cell growth. The imbalanced BCAAs in the diet could negatively affect broiler production. High leucine levels result in increased catabolism of valine and isoleucine and the BCAA deficiency, adversely affecting growth performance of broiler. The objective of the current study was to investigate the effects of additional valine and isoleucine supplementation in a BCAA-imbalanced, high leucine diet on growth performance, carcass and meat yield, body mineral composition, breast muscle quality, decarboxylation of BCAA, breast muscle and jejunal gene expressions, intestinal morphology, litter quality, gait and feather defect scores, and cecal microbiome in broilers. Our data showed that a BCAA-imbalanced, high leucine diet negatively affected chicken growth. Adding valine alleviated the negative impact; however, adding isoleucine exacerbated the negative effects of high leucine diet, further reducing overall growth performance, carcass weight, total tissue weight, fat and lean weight, body mineral composition, breast muscle decarboxylation activity, duodenal villus height, and gait and feather defect scores. These findings further demonstrate the importance of an appropriate BCAA ratio in chicken growth. Leucine, valine, and isoleucine levels must be properly adjusted according to the dietary BCAA ratios for the optimal growth.

Technical Abstract: High leucine levels and an imbalanced branched-chain amino acid (BCAA) ratio in the diet can trigger BCAA antagonism, negatively affecting chicken growth. The current study investigated how additional valine and isoleucine could mitigate the negative effects of imbalanced BCAA diets in broilers. The control and additional isoleucine groups experienced significantly decreased body weight gain (BWG) and feed efficiency compared to the additional valine and valine with isoleucine groups (P < 0.001). Remarkably, the additional isoleucine group significantly reduced BWG and feed intake (FI) compared to the control group (P < 0.001). The additional isoleucine group had the lowest carcass weight, breast muscle weight, lean and fat weights, bone mineral density and content, tight junction-related gene expression levels, and villus height values among the groups (P < 0.05). The additional isoleucine group had the highest levels of breast muscle BCAA catabolism-related enzyme and gene expression among the groups (P > 0.05). However, these values changed similarly to those of the additional valine alone group when valine and isoleucine were provided together. In conclusion, adding isoleucine alone to a BCAA-imbalanced diet can further exacerbate the negative effects of BCAA antagonism and deficiency, impairing growth performance unless additional valine is also provided.