I keep all of my dogs out away from my horses. I had a friend who took her very well behaved pit to another friends farm, this was years ago, but the result is in my brain forever. Pit jumped up and latched on foals nose and wouldn't let go. Pit was killing foal, pit then turned on momma horse and tore her up too. When owner of horses tried to get pit off mare, the pit turned on her. She almost lost her hands and was very torn up. Her husband shot the dog. He had a heart attack from the stress from shooting a dog. He survived, my friend finally healed up, the mare and foal had to be put down. Worst case I ever heard about. This pit was decently bred, family raised and obedience trained. don't know what set off the dog. Any breed can do damage, not singling out pits. My geldings don't like dogs so I am careful for the sake of the dogs as well as the horses. It can go both ways. You have your hands full, glad it wasn't worse and hope it heals well. take care and thanks for sharing, always good to remind folks to be extra careful.