The mother had previous litters successfully and she seemed to be doing well as far as having a nice nest put together and nursing so my first instinct was the male killed them. Are rats one of those animals that the males wont tolerate other males offspring? Because this female was already pregnant when I got her and the father was not my male. That was the only reason I could think of why they would be killed off. The breeder I got them from thinks it was the mother but I'm not sure why. He said his breeders killed off their first couple litters as well when he got started so he separated the mother once pregnant and let her raise them by herself for the first litter and then let them all stay together after that and hasn't had a problem since. I'd just hate to lose another litter so maybe I'll try that with the next litter. I'm just going to run out of room real fast if I need to separate each female.