Female-induced pregnancy block in the golden hamster.

Recently mated female golden hamsters (Mesocricetus auratus) were paired with 12-day pregnant animals for three 10-min periods on 3 consecutive days. Pregnancy success was significantly reduced among subordinate recently mated females whereas litter size was significantly reduced among subordinate 12-day pregnant females. Additional results indicated that physical contact--specifically, defeat by another female--was necessary for blocking to occur. The use of relatively short exposure periods suggests that this effect could occur in the wild.