Effect of Age at Mating on the Prenatal and Postnatal Performance of the Female Rat

Abstract

One-hundred five female rats from 25 litters were either joined with mature males at 3 weeks of age or at 9 weeks of age. Mean age at vaginal opening was about 37 days and was not accelerated by the presence of a mature male. Ninety-eight percent of the younger females pupped. Their average litter size at birth was 8.2. The females joined at 9 weeks had an average of only one more pup born (P < .05) even though they were, on the average, 30 days older (P < .01) and 36 g heavier (P < .01) at parturition than those joined at 3 weeks. This weight advantage was roughly maintained throughout a 3-week lactation. Although pups from the younger females averaged about 2 g less (P < .01) at weaning, it is unlikely that these reduced weaning weights would cause appreciable post-weaning death losses or other husbandry problems. These results indicate that a considerable shortening of the generation interval might be obtainable in selection or inbreeding studies.