Ive been breeding rats and mice for years. I never swap males unless they are getting old. I never have more than 1 male per tub and up to 10 females. I have found that 1.5 to 1.7 works best per tub.Once my mice are ready to be weaned I put all the weanlings into one raise up tub. Freeze the males and IF i need to keep some females for a new colony . Females once adults are never separated since they will kill each other babies if they are not "in the group".

As long as they have water and food Daily they wont hurt each other or their babies.