Effect of glycine equivalent levels in low protein diet containing different SID threonine concentrations on performance, serum metabolites and muscle creatine of broiler chickens.

This study was conducted to evaluate glycine equivalent (Glyequi) requirement in low crude protein (CP) diets with different levels of standardised ileal digestible (SID) threonine (Thr) on performance, serum metabolites, and muscle creatine of broiler chickens from 1 to 21 d age. A total of 1275 one-day-old male Cobb-Vantress chicks were distributed in a completely randomised 3 × 5 factorial arrangement for a total of 15 treatments with 5 replicates of 17 birds each. Diets were formulated to comprise three dietary SID of Thr concentrations 6.9, 8.1 and 9.3 g/kg and five dietary Glyequi levels (12.8, 14.3, 15.8, 17.3 and 18.8 g/kg). An interaction (p < 0.05) was observed between the Glyequi and SID Thr levels for feed:gain and serum uric acid (SUA). With increasing levels of Glyequi, feed:gain decreased linearly (p < 0.05) in 6.9 and 8.1 g/kg SID Thr diets while SUA decreased linearly (p < 0.05) in 6.9 g/kg SID Thr diet. In diet containing 9.3 g/kg SID Thr, increasing Glyequi level optimised feed:gain (p = 0.04) at an estimated minimum level of 15.5 g/kg. Glyequi levels resulted in a quadratic effect (P < 0.05) on BWG, feed:gain, muscle creatine with optimum point of 17.2, 16.7, 17.1 g/kg, respectively. Therefore, minimum requirement of Glyequi in low CP (174.0 g/kg) diet needed to optimised performance is 15.5 g/kg in 9.3 g/kg SID Thr diet, but could be or higher than 20.9 g/kg in 6.9 g/kg and 8.1 g/kg SID Thr diets for broilers. Feeding a low-protein diet of 174 g/kg with adequate Thr concentration at higher Glyequi levels could support performance in broilers of 1–21 d old. Provision of 15.5 g/kg Glyequi in low CP diet containing 9.3 g/kg SID Thr level is required to improve performance. Sufficient supply of dietary Thr concentration represents a sparing effect of Gly especially at marginal levels of dietary Glyequi in low-CP diets. [ABSTRACT FROM AUTHOR]