Why is your male dog afraid of his puppies?

If you mean why a female dog growls at a male when he is by her puppies then its because the female is protective of her pups. Females often growl at other dogs- male or female- as a warning, meaning stay away from my pups. But when she growls at her mate, she is warning him to be careful. If its why the male growls at the female when he goes by the puppies, I'm not quite sure. Probably because he is telling her not to attack him.