Birthing in bitches is a complex process that involves hormonal and instinctive interplay. Most of these hormones are released before and during the birth process. When a dog gives birth, naturally she takes care of the puppies without help from outside sources. She starts by breaking the water sac immediately after the pup is born and then bite off the umbilical cord. She licks the puppies and by instinct ensures they are kept warm and suck breast milk. Bitches naturally eat the placenta and other leftover birth material. Despite these well define natural processes, some bitches eat their puppies and here are the reasons:

1. Accidental Cannibalism: Some bitches while eating the placenta and cutting the birth cord mistakenly eat stillborn puppies. It is suggested that they can’t recognize the hormone of the dead puppies and hence assume it to be part of the afterbirth materials. 

2. Stress: The birthing process is extremely stressful and can lead to bad decisions such as cannibalism.

3. Hormonal Problem: When bitches are unable to recognize puppies as their own due to a problem with hormonal secretion, they can eat the puppies. 

4. If the Bitch was bred too young: Some bitches are too young to be a mother hence showing cannibalistic behaviour to their puppies. 

5. Mastitis: mastitis is a disease of the breast that presents with swelling and pain. When puppies try to suck, the bitch feels excruciating pain and can eat the puppies. 

Cannibalism in bitches is not a common practice. Such dogs are usually tagged ‘Bad mothers’, with the help of your veterinarian, if you can trace the cause, you might be able to help the bitch. It is generally advisable not to breed your dog too early (at first heat) and to monitor your bitches during the birthing process to prevent cannibalism.