Dietary lysine needs of late-developing heavy broilers.

Two studies were conducted to determine the response of late-developing broiler males and females to dietary Lys from 42 to 56 d of age. Hubbard Ultra Yield males and females were placed at separated ends of a floor pen broiler house and raised on common diets. At 42 d of age, broilers were then fed 1 of 7 gradient concentrations of dietary Lys that progressively increased by 0.07% from 0.68 to 1.10% total Lys. Regression analysis was performed to estimate dietary Lys needs in the presence of quadratic responses. Female broilers did not respond to dietary Lys for any variable measured. Gradient additions of Lys improved feed conversion linearly (P < 0.01) for male broilers. Fillet weight, tender weight, and their composite increased linearly (P < 0.05) with Lys supplementation in male broilers. Quadratic responses were exhibited by carcass yield, fillet yield, and total breast meat yield, resulting in total Lys optimization dietary levels of 0.88, 0.93, and 0.93%, respectively, in male broilers. Based on results from this study, high-yield male broilers should be fed a minimum of 0.93% total dietary Lys (0.85% calculated digestible) from 42 to 56 d of age. Lack of response by female broilers suggests that less dietary Lys may be needed for adequate growth and meat yield.