Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/19/2004
Publication Date: 8/1/2004
Citation: Corzo, A., Kidd, M.T., Burnham, D., Kerr, B.J. 2004. Dietary glycine needs of broiler chicks. Poultry Science. 83:1382-1384. Interpretive Summary: The abundance of feed grade methionine, lysine, and threonine results in increased dietary flexibility towards balanced dietary protein levels in broilers. As the understanding of dietary requirements for these amino acids has expanded, levels of dietary crude protein have gradually declined, and consequently, limitations of other amino acids may soon become evident. One such amino acid that may become limiting is dietary glycine. Although glycine has been categorized as a nonessential amino acid in poultry, when low protein diets are formulated in combination with marginal levels of dietary threonine and serine, dietary glycine may become a limiting amino acid. Given that there are excesses of nitrogen-related compounds in a diet, even in birds fed reduced protein diets, and the fact that glycine is necessary to synthesize uric acid molecules in order to excrete excess nitrogen, the level of dietary glycine needs to be evaluated to maintain a minimal level for uric acid formation and optimal production. Experimentation indicated that birds fed a low protein basal diet required approximately 1% dietary glycine to support maximum growth and feed conversion for chicks from 7 to 20 days of age. As such, it appears that dietary glycine should be considered as a limiting nutrient in early chick nutrition, especially if dietary protein is low. As environmental issues with nitrogen losses from poultry operations becomes more pressing and as the availability of crystalline amino acids becomes more economically viable, understanding amino acid limitations in low crude protein diets and their desired concentration in feeding programs for optimal production and minimal nitrogen excretion, is paramount to the broiler industry. Research results described in this report provides nutritionists at universities, feed companies, and broiler production units vital data on the importance of glycine in dietary formulations.
Technical Abstract: Research delineating Gly needs for broilers is sparse. Dietary Gly might become a limiting factor in all-vegetable diets fed to broiler chicks when CP is low. A study was conducted to evaluate dietary Gly needs in broiler chicks from 7 to 20 d of age. Ross 508 male chicks were placed in thirty two floor pens (15 chicks/pen; 5 pens/trt) of a closed-curtain sided house. Chicks were fed a common pre-starter corn-soybean meal based diet (3100 kcal/kg; 23.1% CP; 1.32% Lys) from 1 to 7 d of age, and then fed a titration diet that contained progressive amounts of 0.12% dietary Gly ranging from 0.62% (1.40% Gly+Ser) up to 1.22% (2.00% Gly+Ser) from 7 to 20 d of age. Experimental diets were accomplished by supplementing Gly at the expense of a filler. Using regression analysis (95% of minimum or maximum response), it was calculated that chicks optimized BW gain and feed conversion at 0.98% (1.76% Gly+Ser) and 1.02% (1.80% Gly+Ser) dietary Gly, respectively. Blood plasma free threonine and serine were unaffected by Gly supplementation, but plasma Gly linearly increased. Dietary Gly may need to be considered as a limiting nutrient in early nutrition, especially if CP is low and only vegetable ingredients are used. Present results also suggest that current NRC (1994) recommendations for Gly+Ser of 1.25% may be low.