Well, thanks Jas, I really don't know THAT much about mice, but I know a little. And I seem to get better at it the longer I keep them. I don't think that mice can retain sperm. However, I do know that they can breed immediately after giving birth and can then delay implantation of the fertilized eggs so that it takes longer for them to give birth to their next litter. This can make it seem like the gestation period is taking longer then the usual 21 days.

Mark