They have a different smell
One of the reasons why you should never interfere during a birth is because at this time the female dog forms a special bond with her puppies through their sense of smell. Therefore, if a person touches the pups with their bare hand, they’ll leave traces of their “scent” on the puppy’s body, which will cause the mother to consider the puppy an “intruder” and growl at them.
The age at which puppies can be separated from their mother is after two months of age. If, for some reason this process doesn’t take place and the mother continues to nurse her pups, it’s normal for her to become aggressive and bark at her puppies when they try to get close to her breasts.
This is a natural behavior that shows the puppies they should begin to fend for themselves. However, it isn’t commonly observed, because, in most cases, people separate the little ones from their mother before it happens.
The maternal instinct of female dogs
The maternal instinct is present in all species that provide parental care to their offspring. In the case of dogs, the most distinctive feature is how protective the mother is of her puppies: she always keeps them by her side and doesn’t usually let anyone get close to them.
In addition, puppies are totally dependent on the mother until they’re 2 weeks old, which is when they start to develop their senses. Until this time, the bitch will keep them warm, nurse them and lick them to groom them and stimulate their digestive system, otherwise they wouldn’t have bowel movements.
During the puppies’ third and fourth week of life, they become more independent and the weaning period begins. When they’re able to move on their own and eat solid food, their mother will be their guide to learn how to socialize and forage for food.
Refusing to nurse her puppies
There may be several reasons why a mother dog will not want to nurse her puppies when she knows for a fact that they are totally dependent on her.
If your mother dog is in pain, then she will stop nursing her puppies.
If the puppies continue to go near her, which they will CERTAINLY, and while still in pain, then she will be aggressive with them.