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Responses of broilers to increasing dietary glycine when fed reduced or low crude protein diets from 0 to 48 days

Lee, T., J. Lee, C. Ruan and S. Rochell

Two experiments evaluated broiler performance and processing charac-eristics when fed increasing Gly concentrations in reduced (RCP) or low CP (LCP) diets from 0-48 d. Ross 708 male off-sex chicks reared in floor pens (21 birds/pen) were used in experiment 1 (EXP 1; 1,008 chicks) and 2 (EXP 2; 1,260 chicks). EXP 1 included 4 treatments: a control (CTL) diet and a RCP diet (~1.7% unit CP reduction) without or with Gly added to achieve 100 (moderate; M Gly) or 112% (high; H Gly) total Gly+Ser of the CTL diet in each phase. EXP 2 included 6 treatments: a CTL diet, a RCP diet, or a LCP diet (~2.4% unit CP reduction and 88% total Gly+Ser; LCP88) without or with Gly added to achieve 100, 112, or 124% total Gly+Ser of the RCP diet. Both EXP included starter (0-14 d), grower (14- 28 d), and finisher 1 (28-39 d) and 2 (39-48 d) diets with similar digestible essential amino acid levels. Treatments were replicated in 12 pens in EXP 1 and 12 or 9 pens in EXP 2. Dietary nutrients met breeder specifications. Body weight gain (BWG), feed intake (FI), and FCR were evaluated, and 6 birds/pen were randomly selected for processing at 48 d. Data from EXP 1 were analyzed by a 1-way ANOVA and Tukey’s means separation, while data from EXP 2 were analyzed by pre-planned orthogonal, linear, and quadratic contrasts (P≤0.05). In EXP 1, 0-14 d broiler performance was similar (P>0.05) among treatments. From 0-48 d, broilers fed the H Gly diet had the lowest (P=0.006) BWG and highest (P=0.003) FCR. Feeding either the RCP or M Gly diet resulted in growth and processing yields similar (P>0.05) to the CTL. In EXP 2, increasing Gly in the LCP88 diet linearly reduced (P≤0.027) 0-14 d FI and FCR with no effect on BWG. From 0-48 d, broilers had similar (P>0.05) performance when fed the CTL or RCP diets, but had a higher (P<0.001) FCR when fed the LCP88 diet. Increasing Gly linearly reduced (P=0.033) FCR. Total breast meat yield was reduced (P≤0.02) for birds fed the LCP88 diet relative to that of CTL and RCP-fed birds and did not respond to increasing Gly.

Cumulative data from these 2 EXP indicate that Gly needs of broilers reared to market ages may depend upon dietary CP content per se or other dietary changes associated with low CP diets.