Reproductive and lactational performance of rats bred at different ages

SummarySeventy-two female rats were randomly allotted to three groups and mated at average ages of 44, 63, and 82 days. One half of each age group was killed at parturition and the other one half at day 16 of lactation. Although rats in the youngest age group weighed less than those in the other two groups at each weighing, these age and weight differences did not significantly affect litter weight or number of pups per litter at birth. The oldest rats had more total mammary DNA at parturition, but no significant difference existed by the 16th day of lactation. Total RNA doubled during lactation for all three age groups, but there was no significant difference among age groups at parturition or at day 16. Average litter weight gains were not significantly affected by age at mating, indicating that rats bred as early as 40 days of age lactated and raised litters as well as rats bred after 60 days of age.