[Studies on the pheromonal pregnancy block in the mice. I. Strain differences of mice in pheromonal pregnancy block (author's transl)].

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 approximately 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 pheromone showed strain differences among different strains of mice.