number of baby mice in litter

Question
Today August 12th at 10pm, one of first time mother mice gave birth like I expected her to (I keep a calendar for the mice). Well any ways she only gave birth to 4 babies. Is this normal? (most of my mice actually do have 8-10 babies, one gave birth to 12, but only 11 lived)

I have another female that I bred to the same male and if she has less babies than she did when she did the first time (this is a second time for her). Could it be the male causing so few babies.

So is it normal for the first time mom to have 4 babies?
and could it be the male that is causing her to have so few babies?

Answer
Dear Rachel,

I once had a mouse named Chocolate, who for almost 2 years had a litter of babies every third Sunday.  She averaged around 8-10 per litter but she once had 18-- 14 survived (but she twice weaned 16 of 16)-- and once she birthed just 1 very fat and happy baby.  Four is not a number to worry about.  In fact, the fewer the pups in a litter, the healthier each one will be, because there will be lots of milk and mother love.  

Certainly it is possible that a male have a lower sperm count, and therefore there may be fewer babies per litter.  Also the mother may have some of her uteruses (one for each baby!) out of order for some reason (a cyst, perhaps).  I'm not a mouse gynecologist, so I'm sure there are other possibilities. I suggest you wait and see what happens to her and his next few litters.  Good luck and have fun!

squeaks n giggles,

Natasha