In over forty years of earning my horsemanship chops, I had never heard of it. Had a client with a late teens gelding that was exhibiting EXTREME bad ground manners. Was a peach on the lunge line (if you could get the surcingle on)! He was a rescue and came with the warning that “he gets abscesses frequently.” I was horrified by that as it shouted hoof neglect to me – his feet were in pretty bad shape when she brought him home (rescue).
Anyway, we figured this guy had medical issues going on so got him on a proper diet, wormed and vaccinated him, had his teeth floated (vet said they weren’t too bad), and of course had the farrier out post haste. I was training him on the ground only because he was so underweight for a while. The thing is, he never once took a lame step!
Fast forward a month: He’s only slightly better with ground manners, still a HUGE pain in the butt to get him to take a bridle, and would break out of the cross ties any chance he got. I finally had had it. We had addressed all of the physical issues we could find, and had been taking great pains that we weren’t scaring him or otherwise exacerbating some emotional injury or fear issue he may have been hiding. His behavior just wouldn’t improve.
Finally, when he broke out of the cross ties, I got some help and got him caught. Then I took him back to his stall and asked my helpers to assist with holding him. I wanted to put the bridle on to let him know that breaking away wasn’t a good way to escape the lesson being imparted. He fought way more than he should have, (by this time the vet had been out numerous times and assured us there was nothing wrong with his teeth, face or mouth that should have caused this) and I got irritated and slapped him on the neck and yelled, “Knock it off!” Well color me surprised when he relaxed, dropped his head and took the bit like a gentleman. Then the next day when I went to turn him out, I opened the stall door with a halter and lead in my hand and he BLEW out of the stall, over me, knocking me to the ground. No idea what brought that on but the owner was there and she was certain he was now afraid of me. You had to be there, but believe me when I tell you I did nothing whatever to frighten this horse. Unfortunately, the owner was horrified that I would “hit” her horse (the day before), and promptly fired me. That was a little hurtful, especially since he’d just tried to kill me, but part of the job. It’s her horse and her call. So we actually parted friends. She said she was going to try a natural horsemanship trainer. I wished her the best of luck.
Two weeks later she called me. It seems the horse was getting worse, not better with the new training paradigm. He had gotten to the point that she was afraid of him and wanted him gone. I told her I would check with some rescues and trainer friends and see if anyone would take him. Before I had a chance to do that, I got a call about 3 days later. She told me that she was going to have him put down. I was shocked! I said, no, wait until I can find him a home. She told me that she had the vet out for one last chance to see if we had just somehow missed a pain problem. Well, boy had we. The vet that had been treating him took x-rays of his hind feet on that last visit. The horse that never took a lame step STILL had abscesses in both back feet. This is what made the vet suspicious. The x-rays confirmed, he had a quittor. I had never heard of such a thing so I Googled it and discovered that it is a bone infection that stems from chronic untreated abscesses. It can be cured with long term antibiotics and diligent care of the blown abcesses, but the vet felt that this poor horse had been dealing with it for a very long time. It was his advice to put him out of his suffering. (Not a young horse.) He had been in horrific pain and was trying to tell us the only way he knew how.
Moral of the story? If all normal training methods do not work, there is something physical going on with the horse, no matter how empty all the vet work may be coming up. Don’t stop looking! This whole episode was a CF from the get-go and I feel horrible about it. There is always stuff to learn. 
