Effects of Imbalances or Antagonisms among Nonessential Amino Acids on Growth and Nitrogen Utilization by Rats

A series of studies with weanling rats was conducted to determine the effect on growth rate and nitrogen utilization of adding various combinations of nonessential amino acids to a methionine-supplemented, 14.3% casein basal diet. Amino acids were added at levels to make the diet resemble a 30.5% gelatin diet with respect to the amino acids added. The addition of 7.1% of glycine to the basal diet resulted in a reduction in growth rate of about 20%, whereas the addition of 4.0% of hydroxyproline or 3.0% of proline had smaller and inconsistent effects on growth rate. The concomitant addition of glycine and the 2 imino acids caused a much more severe depression in growth rate which was not altered significantly by supplemental arginine, alanine, or glutamic acid but was partially alleviated by the addition of aspartic acid or serine, or more effectively by a combination of these 5 amino acids. Efficiency of nitrogen utilization was greatly decreased by supplemental nonessential amino acids, but efficiency of feed utilization for the 20-day studies was not altered significantly by dietary treatment.