Dietary glycine plus serine and threonine effects on performance, creatine muscle content and meat lipid oxidation of broiler chickens from 21 to 42 days of age

The study was carried out to evaluate the effects of glycine+serine (Gly+Ser) and threonine (Thr) levels in low crude protein diets on performance, creatine muscle content and meat lipid oxidation (malondialdehyde concentration) of broiler chickens from 21 to 42 days of age. A total of 1,275 21-d-old Cobb male broiler chickens were distributed in a 5 × 3 factorial arrangement consisting of 5 replicates of 17 birds each. Treatments consisted of 5 dietary total Gly+Ser levels (1.38; 1.48; 1.58; 1.68 and 1.78%) and 3 dietary levels of standardized ileal digestible (SID) Thr (0.58; 0.68 and 0.78%, corresponding to 85, 100 and 115% of the required SID Thr, respectively). Interactions were observed (P<0.05) between dietary Gly+Ser and SID Thr levels for ADG and creatine muscle content. Increasing dietary Gly+Ser levels increased linearly (P<0.05) the ADG and creatine muscle content in birds fed 0.58 and 0.78% SID Thr diets, respectively. There were quadratic effects (P<0.05) of Gly+Ser levels on ADG and carcass yield in broilers fed 0.68% SID Thr diet with an optimization level of 1.62 and 1.60% Gly+Ser, respectively. Increasing dietary Gly+Ser levels resulted in a decreasing linear effect (P<0.05) on abdominal fat content and meat lipid oxidation while quadratic effect was observed on creatine muscle content and relative breast weight with optimization point estimated at 1.69 and 1.60%, respectively. Diets containing 0.68% SID Thr improved (P<0.05) the ADG and G:F compared with 0.78% SID Thr diet. A minimum of 1.60% of dietary Gly+Ser level is required to optimize the performance, pectoral muscles creatine and meat lipid oxidation of broiler chickens from 21 to 42 d of age fed varying SID Thr levels in low crude protein diets. Low SID Thr levels increased the dietary Gly+Ser requirement for broiler chickens fed low crude protein diets during the grower phase.