Threonine imbalance and the threonine requirement of the chicken

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 less than 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 0.69 to 0.72 percent of the diet when the diet did not contain the imbalancing amino acid supplements. We concluded that the threonine requirement of the chick is higher than previously reported, and is influenced by the amino acid content of the diet.