Nutritional Requirements of the Rat for Reproduction and Lactation

Abstract

Observations in the rat indicate that reproduction has dietary requirements as great qualitatively as lactation and that there are no specific dietary factors needed for lactation only. Birth wts. were detd. in litters born to mothers on stock and exptl. diets. The young were divided into 2 groups. Group I comprised young born in surviving litters, and Group II included litters in which none of the young survived the lactation period. The avg. wt. of the surviving group was 16.3% greater than that of the nonsur-viving group. The surviving young, distributed according to birth wt., were grouped largely about the avg., while nonsurvivors were more scattered. In survivors, 74.3% weighed over 5.4 g., and only 4.1% weighed under 5.0 g. A study of the wts. of litters at birth showed no relationship between these figures and the number of young in a litter. While some young survived as long as 12 days, most were eaten or died by the 3d day of lactation. Deaths during this period of 3 days can be traced to the reproduction process. Regardless of diet, the survival of newborn rats was dependent largely upon their birth wts. It is proposed that the wts. of the young at birth be used as the first indication of the adequacy of a diet and, further, that lactation success in rats be calculated on the basis of those young and litters surviving on the 3d day of lactation.