Digestible isoleucine-to-lysine ratio effects in diets for broilers from 4 to 6 weeks posthatch

Abstract

SUMMARY An experiment was conducted to evaluate the digestible Ile:Lys ratio (%) in finisher (28 to 42 d of age) phase diets fed to broilers, based on live performance and carcass trait responses. A total of 1,248 Ross × Ross 708 male broiler chicks were randomly allotted to 8 dietary treatments varying in digestible Ile:Lys ratios. A feed made exclusively with conventional ingredients served as a positive control. Digestible Ile:Lys ratios ranged from 57.8 to 74.4% with increments of approximately 2.8 percentage points, and a positive control was formulated to have a ratio of 67%. Step-wise regression analysis did not allow for the calculation of an optimal digestible Ile:Lys ratio for any of the parameters evaluated; thus, means separation was used to analyze treatment effects. No significant differences were observed among treatments for BW gain. However, feed conversion and feed intake were significantly lower for the control diet, which had a considerably higher CP level. An irregular response was observed for feed intake that was due to the dietary Ile:Lys ratio; however, we conclude that feed conversion improved when the ratio approximated 68.9%. No effect was observed for carcass weight or yield among dietary treatments. The digestible Ile:Lys ratio did not affect breast meat weight, but differences were observed in breast meat yield. The diet with a digestible Ile:Lys ratio of 71.7% resulted in improved breast meat yield and was observed to be similar to the control, despite the difference in CP. We conclude that a digestible Ile:Lys ratio of 68.9% was adequate for live performance, but a slightly higher ratio may be required for breast meat yield optimization (71.7%).