Sexing Mice

Question
Today I went to the pet store to get some mice. I wanted 2 females and 1 male. I intend on breeding mice for feeders. However, I am having serious doubt that they sexed them right. Maybe I am a bit paranoid. They said they were still young, less then a year.

I guess I can wait 3 weeks to see if they get pregnant or not.

I have looked online on all the pictures about the tear drop of the female and the anus on the male is further apart but honestly I cannot tell. It's very difficult.

Answer
Hi Kate,

This is the best sexing reference I've found:  http://www.thefunmouse.com/info/sexing.cfm

In a sexually mature male (8 weeks, give or take), the testicles will go into the body sometimes, but can't stay there for very long.  Therefore a good way to tell is to watch the suspected mice until they stand on the edge of something, like a food bowl or the edge of your hand, and see if the testicles protrude.  In females there is little if any hair between the anus and genitals, definitely not enough space to house testicles.  If you aren't yet sure about them, keep them separate - it's always better to control breeding wherever you can.  In any case, giving them three weeks *before* mating them will allow you to observe for undesirable traits or illness - temperament and size are big ones in feeders.  Obese mice do not breed as well and neither do ill ones, and a mouse's behavior with you or other mice can make your life easier or harder.  Another reason to wait to breed if you think they are too young is that it's far easier on females to wait to breed them until they are about 3 months old.  This way they're totally done growing and will have a better success with litters.  The ideal breeding range is between 3 and 12 months, after which point litter size seems to decrease.

You are totally welcome to send photos and I can help you sex them.  :)

If you have any other questions just let me know!
-Tam