Okay. I believe I actually just had a hairless mouse show up in one of my litters! I found this really odd. She got her hair, and it was really thin, and it looked like she was wet. I went and looked at them today, and she's almost bald on her back and stomach, with a little hair on her legs and head so far. She just turned 2 weeks old on Friday. Do they normally loose fur this young? She's the runt, and is at least half(Maybe a third) of the size of her litter mates. I actually have them in with the rats, since they both have very small litters (Three and four.) So the runt can get some food.