THE EFFECT OF DIFFERENT PER CENTS OF PROTEIN IN THE DIET

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Abstract
V. Albino rats (originally 180 in 5 groups, I, II, III, IV and Y) were fed throughout life on synthetic diets containing 10, 14, 18, 22 and 26% protein respectively. The order of fertility of both sexes of the parents from highest to lowest % was groups II, I, III, IV, and V. The average number of litters and the average number of young born per pair from largest to smallest was in the same order. The sex ratio was highest in group II, lowest in V, and below normal in all groups. Results indicate a greater prenatal mortality of [male][male] than of [female][female]. The mortality of the young during the nursing period was least in group II and greatest in V. With the exception of group V the mortality of the [female][female] was greater than that of the [male][male] of the same group. A greater postnatal vitality of the [male][male] than of the [female][female] is suggested. Cannibalism did not exceed the normal or vary sufficiently to warrant any conclusions. The weight at birth of the 3d was greater than that of the [female][female] of the same group. In general the weights tended to increase as the protein content of the diet became greater. The % of daily gain from birth to weaning age was lowest in group I and, with one exception, increased to group V with each addition of protein in the diet. The same order of weights found at weaning were, in general, maintained to the age of 280 days. In group II there survived a larger number of young, in proportion to the number born, than in any of the other groups, probably because of greater vigor. In general the rate of growth of the young increased as the % of protein in the diet increased.[long dash] Author''s summary.[long dash]VI. The curve of average weights of 186 rat mothers during gestation changed gradually from a simple curve in group I to a compound curve in group V. This was probably due to an increasing deposition of adipose tissue during the early part of gestation. The maximal weight attained was correlated with the size of the litter born. The average % gained by the mother due to developing young was II, 22.53; I, 22.50; III, 20.87; IV, 14.49; V, 13.43. For each young born the per cents were: I, 9.84; III, 9.80; II, 8.42; V, 7.34; IV, 6.47. The loss of weight of the mothers while nursing was greatest in group I and became less as the % of protein in the diet increased. Data indicate that the quantity and quality of milk secretion was poorest in the group receiving 10% protein and increased as the protein content of the diet increased.

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