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Threonine Imbalance and the Threonine Requirement of the Chicken

Department of Poultry and Avian Sciences and Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853

Experiments were conducted to determine the influence of dietary amino acids on the threonine requirement of chicks. A diet limiting in threonine and containing the equivalent of 20.6% crude protein was imbalanced by supplements of 0.9 to 1.5% L-tryptophan, 3.0% L-serine, a mixture of 2% each, leucine, isoleucine and valine or a 6.0% mixture of all essential amino acids but threonine. All amino acid supplements decreased the growth of chicks, and decreased food intake and/or efficiency of food utilization (P < 0.05). Supplemental threonine prevented these effects in all cases except for 1.5% tryptophan in which the adverse effect of tryptophan was not prevented completely. The threonine requirement of Leghorn chicks was 0.68 to 0.72 percent of the diet when the diet did not contain the imbalancing amino acid supplements. We conclude that the threonine requirement of the chick is higher than previously reported, and is influenced by the amino acid content of the diet.

KEY WORDS: • imbalance • threonine • serine • amino acid • chick

¹ Present address: Alan T. Davis, Medical Research, Rm. K106. Veterans Administration Medical Center, 10701 East Blvd., Cleveland, OH 44106.

Manuscript received 12 July 1982.