Time of mating and associated changes in the vaginal smear of the post-parturient Mongolian gerbil (Meriones unguiculatus).

Most gerbils mating did so within 24 h of parturition, with a peak of activity occurring between 1600-2000 h on Day 0. Vaginal smears showed a gradual reduction both in the total number of cells present and leucocyte dominance, with a concomitant increase in cornification. A significant change to leucocyte and epithelial cell dominance occurred by 0930 on Day 1. The presence of distinctive fragmentary 'spicules', the absence of vaginal spermatozoa in many females showing vigorous mating behaviour, and significant differences between the sperm content at the time of mating (Day 0) and the following morning (Day 1), were associated with the presence of a concealed vaginal plug. The plug, which is quickly formed at the onset of mating, had usually disappeared by the following morning.