My fiance (Wife in about 11 days now) says the only way we can have breeder rodents is if she can pick the pairings, so I let her have fun and so far we have a fairly robust mouse colony, but our rats just keep dying off....
We have only had 2 litters of rats, they either get tumors, mega-colon, pneumonia, or something else that just kills the breeders.
I moved our last litter of rats inside the house from the garage to hopefully keep them from contracting whatever keeps killing the others.