Studies on the Pheromonal Pregnancy Block in the Mice

I. Strain Differences of Mice in Pheromonal Pregnancy Block

Abstract

Strain differences of mice in the “Bruce effect” were examined among five inbred strains; C3H, C57BL/6, BALB/c, CBA and DDY. For mating, 3 virgin adult females were caged together with an adult male at 8-20 weeks of age, and checked daily for copulation for a maximum of 10 days. The females were removed from the male when the vaginal plug was found, and housed with strange or alien males for 8 or 15 days. The “Bruce effect” was evident in C3H, BALB/c, CBA and DDY strains having high percentages of blocked pregnancies on alien males. In contrast, C57BL/6 strain showed no such effect. Based on these findings, it was concluded that “Bruce effect” caused by alien male phero-mone showed strain differences among different strains of mice.