Understanding the interactive effects of dietary leucine with isoleucine and valine in the modern commercial broiler.

ABSTRACT

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 IleLys (52 to 75), ValLys (64 to 87), and LeuLys (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 LeuLys ratio (110) with moderate ValLys (78 to 79) and IleLys (65 to 66) ratios. Poorer BWG and FCR were observed as LeuLys ratio increased while increasing ValLys and IleLys 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 LeuLys ratio. This effect was complemented by increasing IleLys ratio beyond 68. Lower IleLys and ValLys ratios were required to maximize carcass and breast yield at the lowest LeuLys ratio. However, this strategy yielded less meat than providing a high LeuLys 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 LeuLys ratios; however, meat yield can be enhanced by increasing dietary LeuLys along with IleLys ratios.