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A Determination of the Essential Amino Acid Proportions Needed to Allow Rapid Growth in Chicks¹

Poultry Department, Utah State University, Logan, Utah

A series of experiments was conducted to determine how the essential amino acids in a ration should be proportioned to allow the chick to grow at a rapid rate. In the approach used, the level of each essential amino acid in a ration was adjusted until the growth rate was decreased about the same amount when a constant fraction of any essential amino acid was removed. A purified-type ration was fed which contained approximately 9.0% essential amino acids and 2.88% nitrogen provided by a mixture of proteins and amino acids. The ration considered to have the best essential amino acid balance was calculated to contain 1.28% arginine, 0.43% histidine, 1.15% lysine, 1.30% leucine, 0.80% isoleucine, 0.95% valine, 1.33% phenylalanine and tyrosine, 0.20% tryptophan, 0.73% methionine and cystine, and 0.78% threonine. Chicks fed a ration with the natural isomer of these amino acids at these levels gained 25% more weight and their gain/feed ratio was 15% higher than that of chicks fed a ration adjusted to the National Research Council minimum requirement levels. These amino acid levels are not minimum requirements; replacing simultaneously 12.3% of all 12 with an equal level of nitrogen as glutamic acid did not decrease growth rate.

Manuscript received 29 July 1963.