The effects of intromission frequency on successful pregnancy in the female rat.

Abstract

The copulatory pattern of several species of rodents including the rat, mnouse, hamster, and deermuouse (Peroimyscus) includes a series of mounts during which the male briefly inserts the penis into the vagina but withdraws without ejaculating. Ejaculation occurs during the last insertion of a series, when intromission is maintained for a longer period of time. The function of pre-ejaculatory intromissions has previously been investigated from the stantdpoint of the nmale. Beach'-3 postulated that each intromission of the male rat contributed an increment toward the attainment of an ejaculatory threshold; a series of studies developing this model have subsequently been carried out.4--~0