Weaning - the act of substituting other food for the mother's milk in the diet of a child or young mammal.

Usually once the rat pups eyes are open they will follow their mother and try her dry food and her water bottle. They will continue, however, to line up for the milk bar until you remove the mother rat, even long after they really don't need her milk. In the wild, a nursing mother rat would just abandon her litter at some point to force them to wean off her milk. In a captive breeding population you need to do that for her by removing her when her pups are around 4 or 5 weeks old and can do fine without her.