Why does my dog attack puppies?

It sounds like your seeing more than just play that escalated too much. Experiences in puppy-hood influence aggressiveness as adults but genetics/breed/hormones can also play a key role in this problem. Owner temperament is also a very important factor. There are a number of types of aggression, which needs to be identified in order to fix it, as usually aggression is situational. Please contact a qualified trainer who uses positive training techniques.

This link may be a good reading to start. http://www.quickanddirtytips.com/pets...