Effects of glycine supplementation at varying levels of methionine and cystine on the growth performance of broilers fed reduced crude protein diets

S Powell, T D Bidner, L L Southern
Poultry Science 2011, 90 (5): 1023-7
Two experiments were conducted to investigate Gly addition to reduced crude protein corn-soybean meal (C-SBM) diets with varying levels of TSAA achieved by varying Met and Cys. The experiments were conducted with female Ross 708 broilers in brooder batteries from 0 to 18 d posthatching. Treatments had 6 replicates with 6 broilers/pen. Diets in all experiments were fed without or with Gly supplementation to contain 2.32% total Gly + Ser. All diets were C-SBM based and formulated to contained 1.27% standardized ileal digestible Lys supplemented with 0.20% Lys (0.394% Lys·SO(4)) and to meet or exceed the requirement of all nutrients except Met and Cys where appropriate. Experiment 1 consisted of 8 dietary treatments. Three ratios of Met to Cys (60:40, 50:50, and 40:60) were used on a mole for mole basis to achieve 0.063 mol of TSAA/kg of feed and a positive control with Met:Cys of 50:50 at 0.76 TSAA:Lys. Glycine supplementation did not affect ADG or ADFI; however, G:F was increased (P = 0.003) with Gly supplementation. An increase in Cys and a decrease in Met resulted in a decrease (P = 0.028) in ADG but had no effect on ADFI or G:F. In experiment 2, Met was kept constant at a marginal level of 0.45% and Cys was increased in 0.05% increments from 0.35 to 0.50%. Glycine supplementation had no main effect on ADG, ADFI, or G:F; however, Gly increased G:F at the lower levels of Cys but not at the higher levels (Gly × Cys, P = 0.031). A linear decrease (P = 0.071) was found in ADFI with increasing Cys supplementation. These data indicate that Gly increased G:F in female broilers fed suboptimal levels of Met and Cys but not at Cys levels at or above the requirement. This implies that the synthesis of Cys accounts for a portion of the increased G:F observed from Gly supplementation in female broilers fed reduced CP C-SBM diets.

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