What reason will a staffordshire bull terriers turn on their pups?

This is not a very likely scenario as almost all Dogs make Excellent mothers. Dogs will usually only kill their offspring if they are very sickly. This is not a normal behaviour in Dogs and a mum that has killed her offspring should not be bred from again. Possible reasons for cannibalism or killing of puppies are a behavioural abnormality in the mother or the mother having a calcium or nutrient deficiency. If looked after properly, a mother should not kill her puppies.