My mouse wont get pregnant

Question
i have 5 female mice and 2 male mice and about 6 weeks ago i put two of the female with each of the males. I took the females out about two weeks later but i dont think either of them are pregnant one of them was alreay quite large so it is hard to tell if she has put on weight. The other one has put on weight but hasnt had any babies wich she should of done by now. is there any way i can make sure at least one of them gets pregnant?

Answer
Dear Ashleigh,

It might take a week for a male to know a female well enough to impregnate her (or it might take five minutes).  Then she will be pregnant for three weeks.  She might not show until the third week.  Have you given it enough time?

There is no reason not to keep the males with the females until the females are visibly pregnant.  Just know that if the male is in the cage when the babies are actually born, he will remount the mother mouse that same day, ensuring a second litter in 3 weeks time.  Unless you have two impotent males, you are going to have babies soon, and possibly more than you can handle!

A litter of mice can be up to 18 mice, though it is usually between 8 and 12.  They can be sexually active at 4 1/2 weeks.  If you have two females giving birth to two litters you might have 20 babies.  Half will be males and will need to be separated, possibly one per cage, because they fight.  With continued contact, in another three weeks there will be another 20, and then the first set of babies could have litters too 5 weeks later, making an extra 100 babies.  Thus you have about 150 mice in the first two months.  I just want to make sure you know what you are getting into.  You need a good plan for the babies before they are old enough to start mating too.

Here is a link to information about raising mouse babies from my archives:

http://en.allexperts.com/q/Mice-3824/2008/2/mouse-babies.htm

Good luck!

squeaks n giggles,

Natasha