Growth and reproduction of rats on whole milk as the sole diet

Abstract

Several investigators have observed the effects of rearing rats on milk diets. Matill 1 and co-workers especially have studied this problem, using dried milk or concentrated solutions of milk powder for the most part in their experiments.

We have made a limited study of this problem with the following results. Using fresh, raw liquid milk exclusively 2 we have successfully raised 3 male albino rats to full size at maturity, beginning at weaning. This trial was begun August 10, 1922. Each rat was kept in a separate cage with one-quarter inch mesh wire bottom without bedding. The consumption of milk solids by these rats has varied between 35 and 100 grams per week per rat. These rats, however, on repeated trials have failed to exhibit any mating instinct when placed with females from our breeding colony, which were known to be in heat.

In a second experiment begun October 24, 1922, two colonies of rats, each containing 5 rats, with both sexes represented, on wire bottom cages, have not attained the expected size at maturity on the fresh, raw, whole milk diet. Growth was normal for the first 50 to 70 days only. The calculated average consumption of milk solids for each rat has not been as high as in the case of the rats in Experiment 1, kept in separate cages. The females have so far been entirely barren, confirming Mattill's results.

In a third experiment 3 female rats reared to partial maturity on mixed diet, each having reared one litter, were placed in the above colonies on the whole milk diet. To date, one of these rats has littered twice and the other two once, since being placed on the milk diet; for two of these litters the sire must have been one of the male rats raised on the milk diet, but the other two litters may have been sired by a male placed on the milk diet from a mixed ration.