Previous branched-chain amino acid (BCAA) studies have indicated that dietary BCAA excess mitigates the negative effects of their interactions. As diet CP is lowered in diets based on corn and soybean meal, Val and Ile decrease and are least cost pressure points, but Leu increases. Therefore, a study was conducted using Box-Behnken design (BBD) to determine the impact of BCAA antagonism on broiler performance and carcass traits. Thirteen experimental diets were formulated to contain various levels of digestible (dig) BCAA supplementation according to BBD. Inclusion levels for the BCAA were based on ratios to dig Lys and included: 65, 75, and 85 for dig Val; 58, 66, and 74 for dig Ile; and 110, 130, and 150 for dig Leu. Fifteen-hundred and sixty male broilers were distributed across 78 floor pens and offered common starter from 0 to 14 d. On d 15, broilers were randomly assigned to experimental diets and BW gain, feed intake, and feed conversion ratio (FCR) were determined for a 15 to 34 d period. On d 35, 6 birds per pen processed for determination of carcass traits. Data were analyzed for linear, quadratic, and interactive effects.Statistical significance was considered at P≤0.10. Significant interactions (P<0.10) were observed between Ile and Val for BW gain, FCR, and total breast yield and between Leu and Val for total breast yield. Thirty-five d BW gain was maximized when Val was increased to its highest level and Ile was decreased to its lowest level. Observed FCR response displayed reciprocal antagonism between Ile and Val where it was minimized when either amino acid was at its maximal level while the other was at its lowest. Responses observed for total breast yield also displayed reciprocal antagonism between Ile and Val and Leu and Val, where at practical levels (midpoint) increasing Val reduced total breast yield while increasing Ile or Leu increased total breast yield.
Results from this experiment highlight the importance of evaluating potential interactions between amino acids when conducting trials to determine amino acid requirements as well as modification of amino acid levels in broiler diet formulation and their impact on live performance and carcass traits.