I just want to let you know that when my two girls started to attack each other that one actually was VERY sick. I knew something was wrong - I knew she wasn't acting "right and spent a fortune on vet tests, etc that all came back perfectly normal. The vet thought I was absolutely nuts and ran etsts they felt were useless.... I knew my dog and knew something was "off" with her. Sammie died within 6 months of starting the fights. The vet figures she had cancer that we didn't detect with tests and physical exams (I've since found a new vet).

I've heard of this scenario several other times with dogs in my classes and in rescue. Often one dog is sick when these saudden fights erupt.