Determination of the optimum digestible isoleucine to lysine ratios for male Yield Plus x Ross 708 broilers between 1.0 and 4.0 kg body weight

Abstract

The objective of this research was to determine the optimum digestible Ile to Lys ratios for Yield Plus × Ross 708 male broilers based on growth performance and carcass characteristics from approximately 1.0 to 4.0 kg. In order to accomplish the objective, 3 experiments were conducted providing dose-response treatments with increasing digestible Ile to Lys ratios to broilers at different stages of production. Experiments (Exp) 1 to 3 evaluated broilers from 21 to 35, 28 to 42, and 35 to 49 d of age, respectively. Dose-response diets for all Exp were formulated with spray-dried blood cells and crystalline L-Ile to create a gradient of digestible Ile to Lys ratios (0.46 to 0.83). Digestible Lys was formulated at 1.05, 0.95, and 0.87% in all diets for Exp 1 to 3, respectively. Each Exp also contained a positive control (PC) diet that did not contain blood cells or feed-grade L-Ile and was formulated to contain the same dig Ile to Lys ratio as treatment 5. At the beginning and end of each experimental period, birds and feed were weighed by pen to determine growth performance parameters. Broilers were processed (Exp 1 = 9 birds/pen, 36 d of age; Exp 2 = 14 birds/pen, 43 d of age; Exp 3 = 14 birds/pen, 50 d of age) and deboned to determine carcass characteristics. For all Exp, quadratic effects (P ≤ 0.001) on body weight gain (BWG), feed conversion ratio (FCR), breast meat weight (BMW), and breast meat yield (BMY) were observed as digestible Ile to Lys ratios increased. A pre-planned orthogonal contrast was performed between the PC and treatment 5 for each Exp and showed no effect of blood cell inclusion with the exception of FCR in Exp 1 (P = 0.001) and BMY in Exp 3 (P = 0.017). Optimum digestible Ile to Lys ratios for Exp 1 were determined to be 0.640, 0.725, 0.661, and 0.709 for BWG, FCR, BMW, and BMY, respectively from 1.0 to 2.5 kg BW (P ≤ 0.001). iii In Exp 2, optimum ratios were analyzed as 0.665, 0.671, 0.664, and 0.682 for BWG, FCR, BMW, and BMY, respectively, from 1.6 to 3.0 kg BW (P ≤ 0.001). In Exp 3, optimum ratios were 0.625, 0.692, 0.694, and 0.730, for BWG, FCR, BMW, and BMY, respectively, from 2.7 to 3.9 kg BW (P ≤ 0.001). Based on these findings, optimum digestible Ile to Lys ratios were determined to range from 0.63 to 0.73 for growing broilers between 1.0 and 4.0 kg BW.