I have a female rat that I got from the local pet store. when I got her she was about to explode with babies. she had her litter three days later. she has always been on the bottom tub of my rack with no other males. well the babies are almost weaned and she looks prego again. I mean bulging at the sides. well her sister at the pet shop was doing the same exact thing but she gave birth this morning to another litter. again she hasn't been in with a male since before she delivered? is it possible for rats to have two litters from one breeding? or do I have some strange mutated super rats? thanks JOHN