Investigating the effects of glycine and glycine equivalents on meat chicken performance under low protein diets

Low protein diets are being investigated to reduce feed cost and address health, welfare and environmental concerns associated with feeding meat chickens excess dietary crude protein (CP). Low CP diets supplemented with only essential amino acids (AA) have failed to improve performance to that observed with standard CP diets (Dean et al., 2006). The nonessential amino acid glycine (Gly) is believed to become conditionally limiting as supplementation of Gly and essential AA in low CP diets has improved performance (Dean et al., 2006). Threonine (Thr) and serine (Ser) in vivo degradation both produce Gly as a product (Wu et al., 2013). Therefore, the aim of this study was to investigate the effects of supplementing Gly in comparison to Ser and Thr in low CP diets on meat chicken performance. Male day-old Ross 308 chicks (n=528), were fed a common starter diet containing wheat, sorghum, soybean meal and meat and bone meal from d 0 to d 7. On d 7, chicks were allocated to 48 pens of equal weight, resulting in 6 replicate pens of 11 chicks per pen for each treatment. Feed and water were provided ad libitum throughout the trial. Essential AA were supplemented when determined limiting using AMINOChick®2.0 software. The dietary treatments were: a standard CP diet containing meat and bone meal with a CP of 227 g/kg (SP), a LP vegetarian diet with a CP of 191 g/kg (LP) and the LP diet supplemented with Gly, Ser and Thr at two different concentrations, resulting in 8 treatments. The first AA level was to equal the amount of Gly+Ser in SP (16 g/kg), with Gly, Ser and Thr supplemented on an equimolar basis. The second AA level was based on a recommended Gly+Ser level of 18 g/kg suggested by Shutte et al. (1998). Feed intake and weight gain per pen from d 7-21 were recorded and the feed conversion ratio (cFCR) calculated, and corrected for mortalities. The SP diet had significantly lower cFCR compared to LP (1.241 vs 1.351, P < 0.001). Supplementation of Thr to the LP with 18 g/kg Gly+Ser significantly (P < 0.005) improved cFCR by 3.93% compared to the LP diet (1.298 vs. 1.351), but also resulted in significantly (P < 0.02) lower BWG with a difference of 65 g/bird (801 vs 866 g/bird). Supplementation of Gly and Ser at both levels to the LP treatment resulted in no significant improvement in BWG or cFCR. This proposes that the dietary level of Gly+Ser recommended by Shutte et al. (1998) is excessive at this CP level. The data from this study suggests that Thr cannot be supplemented as a precursor of Gly to offset lower BWG associated with low CP diets and that there is no difference between Ser and Gly supplementation.

ACKNOWLEDGEMENTS: We would like to thank Evonik (SEA) Pte. Ltd and AgriFutures for their financial and academic support with encouragement throughout this study.