Observations on the induction of ovulation and expulsion of uterine eggs in the mink, Mustela vison.

In 8 of 12 mink paired for the first time, pairing alone induced ovulation and a short (5 min) interrupted mating led to 8/8 ovulating with normal numbers of corpora lutea. However, in already mated mink, a short mating (Day 7) failed completely or partly (reduced number of ovulations) to induce ovulation. In mink which refused to mate, hCG consistently induced ovulation. In already mated mink (Day 0) a later mating (Day 7), even if interrupted after 5 min, led to expulsion of the first set of eggs, approximately 50% of which were 'lost' by Day 4 and virtually 100% by Day 6. This effect was not produced by pairing without intromission or by treatment with hCG to induce ovulation. It is concluded that copulation is primarily responsible for the loss of eggs from the uterus, although the exact mechanism remains obscure.