But what if he was separated for the last part of the pregnancy up until now and I put him back in there with three week and almost two week old babies that he's never seen? Will he kill them or will it be okay? I know he's got to be lonely all by himself, rats are social animals. Should I wait a week until the first litter is weaned and put the first mother in with him just to be safe? I'd leave her in there for ten days and all the babies would be weaned and in their own cage by the time I put them both back with the first female. Then next litter i'll just leave him.