Studies of the Protein Requirement of the Neonatal Rat

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Abstract
This investigation is part of a series in which changes in protein metabolism of the rat during preweaning development were studied. Using the technique of hand feeding, the intake of the neonatal rat could be accurately measured, thus making it possible to determine the nitrogen balance index. Rat pups were fed from 1 day of age equal volumes of diets containing 9.6% (whole rat's milk), 4.8%, 2.4%, 1.2% and 0.6% rat's milk protein. Weight gain was linearly related to protein intake. Analysis of the data revealed that the neonatal rat has essentially a zero maintenance requirement and utilizes rat milk protein for growth, with approximately 71% efficiency. Neonatal rat pups utilized a diet containing 5 to 6% protein from purified casein as well as a diet containing 4.8% rat's milk protein; however, the pups were not able to handle diets containing higher concentration of protein from purified casein.