Postimplantation pregnancy disruption in Microtus ochrogaster, M. pennsylvanicus and Peromyscus maniculatus

Abstract

The Bruce effect, inhibition of pregnancy by a strange male before implantation was examined in prairie and meadow voles, species in which ovulation induced by copulation and in prairie deermice which are spontaneous ovulators. Some females in all 3 species exhibited male-induced termination of pregnancy after implantation. Incidence in M. ochrogaster was higher than in the other 2 species, but was lower than that (70%) reported by others. Duration of pregnancy and litter size did not differ significantly among conditions and were within normal ranges reported for these species. There were no obvious differences in nature or incidence of pregnancy disruption in induced and spontaneous ovulators, but incidence was very low when compared with effect of a strange male during the preimplantation period. Increased susceptibility to male-induced pregnancy termination may not be a natural concomitant of endocrine events associated with estrus in reflex ovulators.