Duration of mating relates to fertility in mice

In normal mating, house mice vary dramatically in the number and duration of intromissions that precede ejaculation. Also, some proportion of inseminations typically fails to yield litters. The present studies involved systematic observations of matings of females in natural estrus with males of proven fertility. After standardized observation of mating behavior culminating in ejaculation and a sperm plug, females were allowed to produce litters in undisturbed conditions. In two replications, greater numbers of intromissions and a longer latency from first intromission to ejaculation both correlated positively with litter size.