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Further Aspects of Amino Acid Imbalance, with Special Reference to the High Arginine Requirement of Chicks Fed Casein Diets¹

Department of Poultry Science, Rutgers — The State University, New Brunswick, New Jersey

Three trials with week-old chicks were carried out to elucidate aspects of amino acid imbalance.

1. It was found that the addition of an amino acid mixture lacking in several essential amino acids to a balanced lowprotein diet induced an imbalance which was gradually overcome at higher protein levels even when the amount of the amino acid mixture added remained constant at a percentage of the protein.

2. The factorial supplementation of peanut protein at 12 and 24% of the diet with its two limiting amino acids, methionine and lysine, resulted in improved growth at the 12% protein level only when methionine was added. No effect was observed when lysine was added at this protein level. At the 24% protein level, a slight growth depression occurred upon the addition of methionine alone, while a large response was obtained from lysine alone and the addition of both amino acids improved growth still further. This differential response at the two protein levels can be explained in terms of the relatively greater methionine requirement for maintenance at the low protein level versus a relatively higher lysine to methionine ratio required for rapid growth at the high protein level.

3. The high arginine requirement of chicks fed casein-containing diets may be explained in part by the relative excess of amino acids in casein protein when the latter is calculated to contain 16% of nitrogen. Supplementing 15% isolated soybean protein with the amino acids making up the difference between 20% casein protein (N x 6.5) and the 15% soybean protein depressed growth using the latter diet which contained 1.24% arginine; this depression was overcome by adding more arginine.

4. The implications of these experiments in terms of amino acid imbalance are discussed.

Manuscript received 22 April 1960.