Comparative Protein Requirement of the Rat and Mouse for Growth, Reproduction and Lactation Using Casein Diets

Abstract

Rats (159) and mice (102) were observed during the periods of growth, reproduction and lactation when fed diets ranging from 16.3 to 9.4% of protein, supplied by crude casein. The animals were fed ad libitum, and food consumption measured.The minimum protein concentration which supports growth, reproduction and lactation, such as that obtained with several generations of rats fed an adequate diet, was 16.3%. This diet supplied 17.6% of protein calories or 7.0 mg of total nitrogen/Cal.The minimum protein concentration which supports adequate growth, reproduction and lactation in the mouse was 13.6%. This diet supplied 14.7% of protein calories or 5.9 mg of total nitrogen/Cal.Since the “true” digestibility and biological value of the casein were 99.2 and 71.7 respectively, the 16.3% protein diet contained 5.0 mg of net nitrogen/Cal.Reasons are given for suggesting tentatively that the protein requirement for growth in the rat is 4.5 to 5.0 mg of net nitrogen/Cal.