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ARS Home » Southeast Area » Mississippi State, Mississippi » Poultry Research » Research » Publications at this Location » Publication #283085
Title: Digestible isoleucine-to-lysine ratio effects in diets for broilers from 4 to 6 weeks posthatch

Author
item MEJIA, L - MISSISSIPPI STATE UNIVERSITY
item ZUMWALT, C - MISSISSIPPI STATE UNIVERSITY
item KIM, ELIZABETH
item TILLMAN, P - MISSISSIPPI STATE UNIVERSITY
item CORZO, A - MISSISSIPPI STATE UNIVERSITY

Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2011
Publication Date: 12/20/2011
Citation: Mejai, L., Zumwalt, C.D., Kim, E.J., Tillman, P.B., Corzo, A. 2011. Digestible isoleucine-to-lysine ratio effects in diets for broilers from 4 to 6 weeks posthatch. Journal of Applied Poultry Research. 20:485-490.

Interpretive Summary: The ideal protein concept is the need for critical amino acids (AA) to be formulated in a ratio to lysine (Lys), the first limiting amino acid in conventional corn-soybean meal diets which are primarily used in the broiler industry. The use of the ideal protein concept allows for the most efficient utilization of protein in broiler diets by maximizing nitrogen efficiency and retention. One benefit of the ideal protein concept is that once a ratio or percentage relative to the reference AA (Lys) is established for a certain age, one can calculate the requirement for all other AA under a variety of conditions. Isoleucine (Ile) is one of the limiting AA in conventional commercial diets after Thr, which is the fourth limiting. Therefore, the objectives were to determine the digestible Ile:Lys ratio in finisher (28 to 42 days of age) in male broilers. Eight dietary treatments were formulated with varying Ile:Lys ratios. Digestible Ile:Lys ratios ranged from 58 to 74% with a 2.8 increments. A positive control was formulated with 67% Ile:Lys. No differences were observed in body weight gain for the dietary treatments. However, feed conversion and feed intake were found to be significantly lower for the control treatment, which may have been due to a considerably higher crude protein level. Feed conversion was found to be improved at diets containing a 68.9% Ile:Lys. Diets formulated with 71.7% Ile:Lys resulted in improved breast meat yield and was similar to control treatment groups. Based on the results of this study, it was concluded that a digestible Ile:Lys ratio of 68.9% was adequate for live performance but a slightly higher ratio (71.7%) may be required for optimized breast meat yield.

Technical Abstract: 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 alculation 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%).