Interactions of the branched-chain amino acids. 2. Practical adjustments in valine and isoleucine

Reductions in dietary crude protein have potentially allowed for the occurrence of branched chain amino acid antagonism which can negatively influence live performance and carcass traits. Therefore, 2 factorial studies were conducted with the first experiment evaluating valine and leucine interactions during a 32 to 45 d finisher period, while the second experiment evaluated valine and isoleucine interactions during a 39 to 52 d withdrawal period. Valine, leucine, nor their subsequent interaction influenced broiler live performance or carcass traits in Experiment 1. However, a valine × leucine interaction was observed for average woody breast score and occurrence of scores of 1 and 2. This interaction demonstrated that leucine does not increase woody breast in birds fed diets with a valine to lysine ratio of 77, but interaction differences for woody breast severity varied among valine and leucine ratios to lysine. In the second experiment, increasing valine marginally increased feed intake, while isoleucine influenced tender yield. No valine × isoleucine interactions were observed. Within the confines of the levels used in the current study, manipulation of dietary branched-chain amino acid levels had little influence on live performance or carcass traits during the tested growout periods. The occurrence of a valine × leucine interaction on the incidence and severity of woody breast is perplexing and requires more investigation to determine if a successful mitigation strategy could be developed.