With my adult corns, I feed 1-2 large adult mice every week for maintenance. For my breeding girl, she would take 2-3 during breeding season. After laying, there were times I'd give her up to 5 to regain weight. You can feed rat pups but they have a much higher fat content so though you have to feed less, they aren't as good for them. Just like any animal, you don't want them to be too fat.