OLFACTORY BLOCK TO PREGNANCY AMONG GROUPED MICE

Abstract

The incidence of the pregnancy-block causedby alien males was not augmented by increasing the numbers of males to which the female was exposed, but it was reduced by the presence of other females in proportion to their numbers. When females were deliberately crowded during pregnancy an increased susceptibility to disease was noted, but there was no evidence of the hormonal disturbance otherwise associated with such stress. A mild degree of stress was indicated even when the housing conditions were adequate, among mixed populations formed after mating, but not among pregnant females housed together in the absence of males. Pregnancy failure was more than three times as frequent under inadequate physical conditions of housing during Days 1 to 3 after mating, than under standard control conditions.