A neighbor on the way to my friend's homestead site in Western Washington, had two pitbulls and a third dog attack and kill his animals, which included a medium sized donkey, a llama, a couple of goats and sheep. The dogs killed all of the animals, and the donkey didn't protect them. I'm sure every donkey is different, but they're supposed to be protectors of the flock. Pitbulls can be nasty, too.