Dietary glycine equivalent and standardized ileal digestible methionine plus cysteine levels for male broiler chickens fed low-crude-protein diets

This study was conducted to determine the optimum dietary glycine equivalent (Gly(equi)) level in low-crude-protein diets of 181 g.kg(-1) containing varied concentrations of standardized ileal digestible (SID) methionine + cysteine (Met + Cys) for broiler chicks (1 - 21 d old). A total of 1275, 1-d-old Cobb-Vantress (R) male broilers were distributed in a 5 x 3 factorial arrangement with a completely randomized design of 15 treatments with five replicates of 17 birds each. Treatments consisted of five levels of dietary Gly(equi) (14.9, 16.4, 17.9, 19.4, and 20.6 g.kg(-1)) and three concentrations of SID Met + Cys (7.70, 9.0, and 10.3 g.kg(-1)). Interactions between Gly(equi) and SID Met + Cys levels were observed for feed:gain (P = 0.055) and breast meat yield (BMY) (P = 0.017). In 7.7 and 9.0 g SID Met + Cys.kg(-1) diets, optimal feed:gain and increased BMY were observed at Gly(equi) levels not lower than 17.9 g.kg(-1). In 10.3 g SID Met + Cys.kg(-1) diet, a lower feed:gain was achieved at 19.4 g Gly(equi).kg(-1). Therefore, a minimum dietary level of 17.9 g Gly(equi).kg(-1) is needed to increase growth of broilers fed diets containing 7.7 or 9.0 g.kg(-1) SID Met + Cys, whereas 19.4 g.kg(-1) Gly(equi) is necessary in diets containing 10.3 g.kg(-1) SID Met + Cys for optimum growth.