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Optimization of dietary valine to lysine ratios in response to varying leucine to lysine ratios in male broilers from 20 to 34 days of age

Lee, J., A. Corzo, M. Silva, R. Kriseldi, R. Adhikari and C. Williams

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.