Strange Male Block to Pregnancy: its Absence in Inbred Mouse Strains

A SERIES of papers by Bruce and colleagues 1–4 has described a pre-implantation block to pregnancy in non-inbred laboratory mice which is evoked by the presence of strange males of the same strain or of a different strain (‘alien’ males). This effect is olfactory-mediated. The phenomenon has also been reported in another species, non-inbred prairie deermice ( Peromyscus maniculatus bairdii ) 5 .