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Effect of Age at Mating on the Prenatal and Postnatal Performance of the Female Rat¹

University of Wisconsin, Madison 53706

Abstract

One-hundred and 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.

¹ Paper No. 1741 from the Laboratory of Genetics and No. 639 from the Department of Meat and Animal Science. Research was supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and by the Program Project in Genetics, Grant No. GM15422, from the National Institutes of Health.