Lactation Studies at Different Planes of Protein Intake. ∗

Abstract

This is a preliminary report of part of an extensive study of the comparative effects of different planes of protein intake upon female rats with respect to the production of young, lactation, and the resulting condition of both mothers and offspring. Table I shows the rations employed in the present experiments, the dietary adjustments being such as to keep the yield of energy and the content of calcium and phosphorus constant while the protein in one mixture was increased through substitution for part of the carbohydrate in the other.

Rats, under 100 days of age, weighing at least 160 gm. and previously fed alike on the stock ration, were placed on the 2 rations and mated. The male was removed when pregnancy was apparent. When the young were born, they were counted, weighed, and reduced to 6 (3 males and 3 females when possible). The mother and litter were weighed every 3 days until the 20th day, which was chosen as the period during which the weight of the young was a measure of the milk secretion of the mother. On the 22nd day the young were removed from the mother and the latter was remated for a second pregnancy and lactation. In this way each of the females was carried through at least 6 lactations, so that the possible cumulative effects of the diets could be noted.

Table I1 summarizes significant data for the first 6 Iactation periods. The 2 rations have yielded identical averages for the birth weights and litter size. Though the figures for litter size and birth weights vary considerably from one lactation to another there is no certain trend either up or down with succeeding lactations.