Why do dogs kill their newborn pups

I have heard of this happening in several instances, sometimes the *****/gyp/mother dog is just paternally unsound and kills the pups just for the hell of it, I have heard said they see them as competition. Other times if there is something wrong with the pups a good mom dog will cull them out, as they would probably not make it anyway. In rare occasions if the female is in poor condition nutritionally she may eat them for nourishment. What type/breeed of dog if I may ask? Also did she kill and eat them or just kill them?

She is a staffy... the pup was OK this morning but wheni went and checked later on she was holding it in her mouth when I managed to get it off her I notice the side of its face looked like it had been licked off

A lot of times mother dogs will kill their young if they are sick or the mother is not well enough to care for all of their young. How old is your female? Up to date with vaccines, proper 'pre-natal' care?

Another factor is environmental, female dogs may kill their puppies as a response to their environment. For example, if a dog feels that there is not an adequate supply of food, she may kill one or more of her puppies to ensure the survival of herself and the others.

Female dogs may also kill a sickly newborn puppy as a means of preventing the spread of infection to the rest of the litter. For the mother, this has the added benefit of providing her with a meal and therefore averting a trip away from the litter. This may seem cruel to humans, but for the female dog, staying with her puppies for as long as possible is her main priority.

F a female dog feels that her puppies have been contaminated or damaged in any way, she may choose to kill one or all of them.I have actually witnessed this with a litter of GSP's, who were killed after being taken away for tail docking.