Rat-induced disruption of early pregnancy in mice and its prevention by the stud male.

Recently inseminated mice exhibited a high rate of pregnancy failure following exposure to male rats irrespective of whether they were housed in direct physical contact with the rat or not. Pregnancy disruption was also seen in mice which were housed on male rat-soiled bedding. By contrast, inseminated mice housed with female rats or on bedding soiled by female rats showed a significantly lower rate of pregnancy failure. The presence of the stud male prevented the pregnancy failure in mice induced by exposure to male rats or male rat-soiled bedding. This protective effect of the stud male on pregnancy in rat-exposed mice is analogous to the protective effect of the stud male on pregnancy in conspecific novel male-exposed mice and in mice subjected to nutritional stress. Hence the possibility that the protective effect of the stud male on pregnancy in male rat-exposed mice is due to the stimulation of luteotrophic activity by the stud male-originating olfactory cues cannot be ruled out. However, it is not clear whether the pregnancy failure in newly inseminated mice induced by exposure to rats is the result of a general stress or is mediated through rat-originating chemosignals acting interspecifically.