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(P<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.