The effect of litter size on weight gain in mice.

The body weights of rodents at weaning are generally believed to be inversely related to the number of animals in the litter during the birth-to-weaning period. Quantitative data for rats have been published, but not for mice. Using carefully matched litters, we have measured the average body weights of mice raised in litters containing 2, 4, 6, and 12 pups relative to the average body weight of litters of eight pups. Except for the 2 pup litters, the inverse relation was found to hold. It is also shown that the pattern of average weaning weight as a function of litter size is the same as previously published by two other groups using rats.