Years ago, even though the dogs raised together were friends, one of my dogs bit the other dog pretty good. I took the dog to the vet ad the vet told me that she wanted to do a blood test on the dog. Here the dog was going through kidney failure. The vet said it's not uncommon for one dog to go after a sick dog.
Geist- White German Shepherd- 1/2014
Indy- Black German Shepherd- 9/2014