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

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). 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, the gene expression levels in breast muscle decreased 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.