Why do mother dogs eat their children

Newborn dog pups congenital death, deformity, weakness, this time the mother dog in order to ensure the survival rate of other dog pups, not to let the milk waste, will eat that defective dog pups to supplement nutrition. Puppies just born by artificial contact, or indirectly stained with a special smell, the mother dog will also happen to eat the pups, because the dog is relying on the smell to identify the child, found that the child has a different smell will eat, this situation occurs mostly in stray dogs.