if they have access to water then your statement in untrue.
Rats kill offspring when they feel they can not sustain the entire colony, then they weed out the weak.
My building hits 90's most of the summer. Many southern breeder's buildings are not temp controlled.
I would say you either have a bad female or a bad male.
Retry with different breeding stock.
I would take Tom up on his offer if you are capable. He has some good breeding stock....I know, much of it came from me![]()