The pre-ejaculatory behavior of male and female rats affects the number of sperm in the vagina and uterus.

The number of pre-ejaculatory intromissions a female rat receives affects the probability of becoming progestational and transporting sperm into the uterus. We now report that the number of intromissions a male rat delivers affects his ejaculatory performance. Males and females were given different copulatory experience by switching females during mating. When either the male or female had few intromissions, few sperm were recovered and the copulatory plugs fit less well. Intromission-dependent sperm recovery was also observed in a review of 94 copulatory tests drawn from archival data. Several possible mechanisms are discussed, including poor placement of the copulatory plug and reduced sperm output. The potential significance for reproductive success in social mating situations is discussed.