dogs attack

Question
I have 2 adult dogs.One a choclate lab and one a american pitbull female.They mated and now she has 8 puppies.Our american pitbull has been growling at the cats and dog that live in our home.she has attacked the choclate lab several times and he has done nothing to provoke her.Why is this happening

Answer
I don't have any experience with breeding dogs.  You may want to submit your question to the experts in the following category:

http://www.allexperts.com/el/3634-9/Dog-Breeding-Whelping

I have heard, however, that females can be protective of their pups.  It sounds like that may be what's going on.