Influence of increasing glycine concentrations in reduced crude protein diets fed to broilers from 0 to 48 days

Two experiments investigated broiler growth performance and processing characteristics when fed increasing Gly concentrations in reduced CP diets fed from 0 to 48 d. In experiment 1, birds were allocated to 1 of 4 dietary treatments: a control (CTL) diet containing feed-grade L-Met, L-Lys, and L-Thr, a reduced CP (RCP) diet with additions of feed-grade L-Val and L-Ile, or the RCP diet with moderate (M Gly) or high Gly (H Gly) inclusion levels to achieve a total Gly + Ser of 100 or 112%, respectively, of the CTL diet. Birds in experiment 2 were assigned to 1 of 6 dietary treatments: a CTL diet, a RCP diet, or a low CP (LCP) diet without or with added Gly to achieve 88, 100, 112, or 124% total Gly + Ser concentrations of the RCP diet. For experiment 1, 0 to 14 d broiler performance was similar (P > 0.05) among dietary treatments. From 0 to 48 d, broilers fed the H Gly diet had the lowest (P = 0.006) body weight gain (BWG) and highest (P = 0.003) feed conversion ratio (FCR). Feeding either the RCP or M Gly diet resulted in similar (P > 0.05) growth and processing characteristics to the CTL. For experiment 2, increasing Gly levels in the LCP diet linearly reduced (P ≤ 0.027) 0 to 14 d FI and FCR. From 0 to 48 d, broilers had similar (P > 0.05) performance when fed the CTL or RCP diet, but had a higher (P < 0.001) FCR when fed the LCP88 diet. Increasing Gly levels linearly reduced (P = 0.033) FCR. Total breast meat yield was negatively affected (P ≤ 0.020) when feeding the LCP88 diet and did not respond to Gly levels. In conclusion, effects of increasing total Gly + Ser levels on 0 to 48 d broiler performance are likely dependent on the content of dietary CP and other potentially interacting nutrients.