A study was conducted to understand the relationship among dietary
branched-chain amino acids (BCAA) on the performance of Ross 344 × 708 male broilers. A total of 2,592 d-old male chicks were randomly placed into 144-floor pens according to a 23 full factorial central composite design (CCD) with 20 treatments (14 treatments and 6 center points). Each treatment consisted of varying digestible Ile:Lys (52 to 75),
Val:Lys (64 to 87), and
Leu:Lys (110 to 185) ratios. Birds and feed were weighed at 20 and 34 d of age to determine
body weight gain (BWG), feed intake, and feed conversion ratio (FCR). At 35 d of age, feather
amino acid composition and carcass characteristics were evaluated. Data were analyzed as CCD using the surface response option of JMP v. 15.
Body weight gain (1,332 g; P < 0.001; R2 = 0.93) and FCR (1.54; P = 0.002; R2 = 0.88) were optimized at the lowest
Leu:Lys ratio (110) with moderate
Val:Lys (78 to 79) and Ile:Lys (65 to 66) ratios. Poorer BWG and FCR were observed as
Leu:Lys ratio increased while increasing
Val:Lys and Ile:Lys ratios alleviated the poor performance. Carcass (71.5%; P = 0.031; R2 = 0.76) and breast yield (26.7%; P < 0.001; R2 = 0.96) were maximized at the highest
Leu:Lys ratio. This effect was complemented by increasing Ile:Lys ratio beyond 68. Lower Ile:Lys and
Val:Lys ratios were required to maximize carcass and breast yield at the lowest
Leu:Lys ratio. However, this strategy yielded less meat than providing a high
Leu:Lys ratio diet. Dietary BCAA had little effect on altering the composition of feather
protein and
amino acid (P > 0.10). These results suggest that optimum BCAA ratios to Lys may vary depending on response criteria and demonstrate the importance of maintaining proper Val and Ile ratios centered on dietary Leu. Live performance can be optimized in diets with low
Leu:Lys ratios; however, meat yield can be enhanced by increasing dietary
Leu:Lys along with Ile:Lys ratios.