Male-pheromone effect on the efficiency of pregnancy in female mice.

Outbred female mice were exposed during 3 oestrous cycles and mated to outbred or C57BL/kw males. Although ovulation number (CL and flushed eggs) was similar in all females, there were significantly fewer (P < 0.01) fertilized eggs and implantations in females exposed and mated to C57BL/kw males. Exposure to outbred males and mating with C57BL/kw males led to some improvement but the best results were obtained with females mated to outbred males. The activity of uterine dehydrogenases on Day 4 of pregnancy was also greatest in females mated to outbred males. It is concluded that the pheromonal stimulation leads to hormone concentration differences which affect implantation.