Among wild dogs, the mother sets the pace for weaning by spending more and more time away from her pups. This doesn't happen the same way in domesticated dogs, who often aren't given the opportunity to leave their pups for very long periods of time. Human intervention is necessary to complete the weaning process.
Introducing a New Food Source
Puppies don't automatically recognize a new source of food. After all, they've never known anything besides nursing. Help them figure it out by placing a large shallow pan of diluted canine milk replacement on the floor and putting the puppies around it. Encourage them to sniff and paw at it. Some probably will jump in the pan and walk through the milk. Let them explore as much as they want, even though they probably will make a mess and consume very little of the milk. For any puppies who don't get a taste of the milk, either out of the pan or licking it off of themselves or litter mates, place some on their lips using your finger. Do this several times until the puppies begin to drink the milk when it is offered.
When the puppies reach 3 to 4 weeks old, start offering canine milk replacement that has been diluted with water. Mix one part milk replacement and one part water. Use only canine milk replacement, not condensed, cow, goat or any other type of milk. Offer the diluted milk by itself three to four times a day for a week or two, until the puppies are lapping it up consistently with no ill effects, such as loose stools.
After the puppies have grown used to the diluted milk replacement, at 4 to 5 weeks of age, begin adding small amounts of wet puppy food to create a thin gruel. At first the gruel should be comprised mostly of milk and only a small amount of puppy food. Each day add a little more puppy food and reduce the milk by a small amount until, by 5 to 6 weeks old, the puppies are eating canned puppy food without milk replacement.
Once the puppies get their first teeth, usually between 6 and 8 weeks old, introduce dry puppy food. This should be done in much the same way as the introduction of canned puppy food by mixing the dry food in with the wet in gradually increasing amounts during the course of a week or two. It may be necessary to soak the dry food in water for a few minutes prior to feeding until the puppies have a full set of teeth.
Puppies will continue to nurse as long as the mother will allow it, even when they are getting most of their nourishment from other food. After about six weeks it may be necessary to separate the puppies from the mother to stop them from nursing. This way the mother can regain her strength and get back to a healthy, pre-pregnancy condition.