Standardized ileal digestible lysine requirements based on growth performance and histochemical characteristics of male broilers from 10 to 21 d of age.

The growth performance and histochemical characteristics of breast muscle fibers were used to estimate the standardized ileal digestible (SID) Lys requirements for 10- to 21-d-old male broilers. Three hundred and sixty 10-d-old Ross 308 broilers (290 ± 16.6 g) were allocated to 6 diets in a randomized complete block design with 6 replicate cages per treatment and 10 birds per cage. The 6 experimental diets were formulated to contain equally spaced increasing levels of SID Lys from 0.86% to 1.36%. The data were analyzed using the MIXED procedure of SAS. The Lys requirements were estimated by the NLIN procedure of SAS. An increase in dietary SID Lys from 0.86% to 1.36% resulted in a quadratic increase ( < 0.05) in body weight gain (BWG), gain to feed ratio (G:F), breast weight, muscle cross-sectional area (MCSA), and fiber area. The SID Lys requirements based on the one-slope broken-line, quadratic line, the first intercept between the plateau of the one-slope broken-line and quadratic-line models and 95% of the upper asymptote of the quadratic-line model were estimated to be 1.01%, 1.19%, 1.08%, and 1.13% for BWG, 1.06%, 1.22%, 1.11%, and 1.16% for G:F, 1.10%, 1.29%, 1.19%, and 1.22% for breast weight, 1.06%, 1.22%, 1.12%, and 1.16% for MCSA, and 1.14%, 1.22%, 1.16%, and 1.16% for breast muscle fiber area, respectively. It was concluded that the SID Lys requirements for broilers at the age of 10 to 21 d depended on the response variables used for estimation, and that histochemical characteristics of breast muscle fibers could be good indicators for estimating SID Lys requirements.