The Role of Glycine in Chick Nutrition

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Abstract
The effect of 4% glycine supplementation to diets low in niacin and vitamin B12 was studied. Under the conditions of our experiments, glycine did not depress growth when fed in excess of 4% to diets already containing at least 1 to 1.5%. Instead, it significantly improved feed utilization, a phenomenon which decreased with advancing age of the birds. This better efficiency could be explained by significant increases in the percentage of feathers and muscle creatine levels in the glycine-supplemented chicks. The importance of glycine for creatine synthesis is accentuated by the fact that the muscle creatine content in early chick life is extremely low. The rise in muscle creatine content with age may be related to the decreasing difference in feed utilization due to glycine supplementation. The glycine requirement for optimum growth and feed utilization of fast-growing birds is in excess of 1.5% both in purified as well as practical starting rations.