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Biological Values of Six Partially Purified Proteins for the Adult Albino Rat

Division of Animal Nutrition, University of Illinois, Urbana

The digestibilities and biological values of 6 protein sources of widely different nutritional quality (whole egg, egg albumin, beef, casein, wheat gluten and peanut flour) were determined with adult male albino rats by the nitrogen balance method. Four of these protein sources were also tested with young growing rats. The results have been compared with those secured by Hawley and associates ('48) with adult human subjects, with the same protein sources and by a nitrogen balance method.

The digestibility of the proteins does not differ greatly for growing rats, adult rats and adult humans, but the biological values are quite different for those proteins deficient in cystine-methionine (beef, casein, peanut flour) or in lysine (wheat gluten).

On the basis of this experiment, supported by other data, it may be concluded that the cystine-methionine requirement of the adult rat is more intense, in relation to requirements for other amino acids, than that of the growing rat or of the adult human. On the other hand, the lysine requirement is much less. These differences may be explained on the basis of the amino acid composition of hair and the relative importance of hair growth in the protein nutrition of the growing rat, the adult rat and the adult human.

Except for differences in the proportional requirements for cystine-methionine and lysine, the dietary nitrogen requirement for nitrogen equilibrium is of the same order of magnitude for adult rats and adult humans when expressed as milligrams of nitrogen per calorie of basal metabolism.