Transcervical sperm transport in the rat: the roles of pre-ejaculatory behavior and copulatory plug fit.

In the rat, the transport of sperm from the vagina, where they are deposited at ejaculation, into the uterus is not automatic. Various behavioral and physiological factors influence this transport process: the number of pre-ejaculatory intromissions, the duration of immobility at ejaculation, and the fit of the copulatory plug. The interplay of these three factors in producing adequate sperm transport, and their relations with each other, were examined in 52 female rats that received various numbers of pre-ejaculatory intromissions (from 0 to more than 15). The number of intromissions was strongly related to all other measures. Ejaculatory immobility was associated with better fitting copulatory plugs when females received few intromissions. Sperm transport was most strongly predicted by plug fit. Intromissions were a major predictor of good fitting copulatory plugs and transcervical sperm transport; immobility did not mediate intromission's influence and did not have a major independent role.