A study was conducted to determine the optimization ratio of valine to lysine dependent on dietary leucine to lysine rations with a fixed isoleucine to lysine ratio on live performance and carcass traits in Ross 344 × 708 male broilers from 20 to 34 days of age. A total of 1,080 d-old male chicks were randomly placed into 72-floor pens according to a 2n=2 full factorial in central composite design (CCD) with 12 runs (8 treatments + 4 central points) and 6 replicates per run. A common feeding program was adopted until 20 days of age. Subsequently, each pen received 1 of 9 dietary treatments from 20 to 34 days of age varying in digestible ratios of Val:Lys (70 to 86) and Leu:Lys (90 to 192) which were calculated according to their corresponded code matrix values (-, -1, 0, +1, +). Digestible Ile:Lys ratio was fixed across all treatments at 68. 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 were processed to determine carcass characteristics. Data were analyzed using JMP v.15 by adopting the response surface macro option. Body weight gain (1547 g; P = 0.15) for the period was optimized at a Val:Lys ratio of 85 and a Leu:Lys ratio of 108. Feed conversion ratio (1.498; P = 0.003) from 20 to 34 d of age was optimized at a Val:Lys ratio of 81 and a Leu:Lys ratio of 116. Poorer BWG and FCR were observed as Leu:Lys ratio increased although increasing Val:Lys ratios partly alleviated the poor performance. Breast weight (633.9 g) was maximized at a Val:Lys ratio of 86 and a Leu:Lys ratio of 103. Conversely, breast yield (27.12%) was maximized at a Val:Lys ratio of 70 and Leu:Lys ratio of 192. Interestingly, live performance (BWG and FCR) was optimized at the lowest Leu:Lys ratios while breast meat yield was optimized at the highest Leu:Lys ratio indicating that BCAA influence body composition.
These results revealed that optimum Val:Lys ratios vary depending on the desired response criteria and to the level of dietary Leu:Lys.