A central composite design (CCD) study was conducted to understand the relationship among dietary branched-chain amino acids (BCAA) on live performance, carcass traits, and feather composition in Ross 344 × 708 male broilers. A total of 2,592 d-old male chicks were randomly placed into 144-floor pens. Each pen received 1 of 16 dietary treatments from 20 to 35 d of age varying in digestible ratios of Ile:Lys (52 to 75), Val:Lys (64 to 87), and Leu:Lys (110 to 185) arranged as CCD. 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, all birds except 1 were processed to determine carcass characteristics. Feather dry matter, protein, and amino acid compositions were determined from the last 5 primary feathers of 1 bird per pen. 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) from 20 to 34 d of age were optimized at the lowest Leu:Lys ratio (110) with minimum Val:Lys (78 to 79) and Ile:Lys (65 to 66) ratios. Poorer BWG and FCR were observed as Leu:Lys ratio increases although increasing Val:Lys and Ile:Lys ratios alleviated the poor performance. Opposite to live performance, both 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. In contrast, it requires lower Ile:Lys and Val:Lys ratios to maximize carcass and breast yield at the lowest Leu:Lys ratio but with lower meat yields than in high Leu:Lys ratio. Feather protein content was the highest (96.1%) when increasing Ile:Lys ratio to 70 (P = 0.07) with Leu:Lys and Val:Lys ratios of 110 and 80, respectively. Increasing Leu:Lys ratio to 185 decreased maximum feather protein content to 93.5%.
These results revealed that optimum BCAA ratios to Lys may vary depending on the desired response criteria and demonstrate the importance of maintaining proper Val and Ile ratios dependent 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.