The Food Intake and Nitrogen Retention of Weanling Rats Fed Protein-Free Rations

Variations in the food consumption of weanling rats, fed rations containing a mixture of indispensable amino acids and diammonium citrate, were largely associated with the apparent digestible energy (A.D.E.) content of the diets. The influence of bulk (as measured by dry density) on food intake could not be entirely resolved but there was some indication that the influence of dry density on food consumption resulted from its high association, in these experiments, with the A.D.E. content of the food. The gross nitrogen level of the rations, and hence the diammonium citrate content, did not exert any significant influence on food consumption. The ratio of A.D.E. to apparent digestible nitrogen (A.D.N.) was associated with 65% of the variance in the percentage A.D.N. retained. This relationship was curvilinear yielding an estimated maximum for the A.D.N. retained of 65.2% with the A.D.E. per gram A.D.N. at 264 Cal. The importance of A.D.E. in determining the biological values of proteins or nitrogen sources was discussed. It would seem necessary to determine biological values when the ratio A.D.E.: A.D.N. of the food results in the percentage of A.D.N. retained being situated on the plateau of the curve. Perhaps the most accurate data would be obtained when the A.D.E. per gram A.D.N. results in a maximum percentage of A.D.N. being retained.