Reproductive capacity of male laboratory rats.

The purpose of this research was to investigate the reproductive capacity (i.e., the ability to successfully transfer an ejaculate and induce a progestational response in the female) of male laboratory rats (Rattus norvegicus). Males were individually mated to successive females in a single session for one ejaculatory series each. There was a marked decline in both the total number of sperm per ejaculate and the number of sperm transported to the uterus with repeated ejaculations. Dimensions of the copulatory plug of the male decreased over successive ejaculations, reflecting a diminished output of the secretions of the reproductive accessory glands. Male copulatory behavior changed over successive ejaculations. Actual fertility appeared somewhat diminished in late ejaculatory series. Such constraints on the reproductive capacity of the male may have implications for the mating strategy employed by wild males in the field.