Problems of undernutrition research with breeding mice.

Rats undernourished throughout pregnancy and lactation lose few young during the suckling period and wean normal size litters of extremely growth-retarded offspring. Comparable treatment of maternal mice, on the other hand, resulted in considerable nestling mortality. Thus few young were reared to weaning and these were not nearly as growth-retarded. Detailed evidence is given of the effects of different schedules of undernutrition throughout pregnancy and lactation on the reproductive performance of mice. These findings are compared with those for rats and possible reasons for the difference in nestling mortality discussed.