Effect on Chick Growth of Amino Acid Imbalances in Diets Containing Low and Adequate Levels of Niacin and Pyridoxine

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Abstract
Amino acid imbalances were produced in chick diets by the addition of 4% of single amino acids to diets low and adequate in niacin and pyridoxine in which the protein was furnished by 18% crude casein, 5% gelatin, and 0.3% DL-methionine. When L-arginine HCl, L-leucine, glycine, DL-aspartic acid, L-glutamic acid, or a DL-threonine-DL-allothreonine mixture was added to a diet adequate in niacin and pyridoxine, the growth rate of the chicks was not depressed. Additions of L-proline or DL-alanine decreased the growth rate slightly. Additions of DL-valine, L-cystine, DL-isoleucine, L-tyrosine, L-histidine HCl, DL-phenylalanine, DL-tryptophan, L- or DL-lysine HCl, or DL-methionine markedly decreased the growth rate. All amino acids depressed growth when added to a niacin-low diet; only DL-threonine-DL-allothreonine caused a growth depression when added to a pyridoxine-low diet, and this could be overcome by the addition of pyridoxine. The amino acids were divided into two groups on the basis of their effects on growth. One group included valine, tyrosine, phenylalanine, isoleucine, tryptophan, lysine, and methionine. The addition of these amino acids or mixtures of these amino acids to the chick diet depressed growth more than the other amino acids, and the growth depression was not greatly influenced by the addition of niacin to the diet. The other amino acids when added to the niacin-low diet caused a growth depression which was partly or entirely overcome by the addition of niacin to the diet. Additions of amino acids to a diet containing adequate niacin increased the fasting blood sugar level of chicks, but additions of L-arginine HCl, DL-alanine, DL-aspartic acid, L-glutamic acid, or glycine to a niacin-low diet decreased the fasting blood sugar level. The blood amino nitrogen level was increased by the addition of each amino acid except methionine, lysine, and arginine. Possible mechanisms by which the amino acids cause these effects are discussed.