I guess I can't say my horse was harmed in the sense of injury, but it certainly made me angry. The farm I used to both board and work at, I kept my then mare, a TWH/Friesian cross mare. She was gorgeous, jet black with mane close to 45 inches long and a tail that drug the ground by several inches. One day I showed up and walked into my mare's stall and had to stop, stunned. Her tail was a chopped off bob about 1 inch longer than the bone, and her mane had huge chucks missing out of it. I flew down to the office, furious, to find out what happened, to find everyone shugging their shoulders. The BO said he believed the appy in the next stall, a spoiled horse belonging to a little old lady, had chewed my horses mane and tail off. The stalls were good size - about 12x12, and had tongue and groove until about 4 ft and then wire on top separating. My mare was a little on the witchy side. Even if the horse next door could have got a mouthful of hair, I don't believe she would have stood there against the stall wall for the HOURS it would have taken for him to munch it all off, especially at the tail where there was NOTHING left. The parts of hair were suspiciously straight, and not matted with saliva or otherwise appearing chewed. I knew it was ridiculous but what could I do? The BO also told the owner of the appy that they believe it happened - the poor old woman was very beside herself and called the vet out, who also stated she didn't believe the appy had ate the mane and tail. She (the vet) also took me aside to tell me in low tones that long, black horsehair is valuable for extensions, hatbands, etc.
I told them I was going to take my horses from the property. This is when I found out things even worse about them. I had recently bought a mare from another boarder, one who had been used by the BO as a trail horse, but would have been an ideal lesson horse for me. When I said I was taking her too, they tried to stop me, telling me they had bred her to their paint stallion and that they had a right to the baby. Since I hadn't had any knowledge of this, and I had not given them permission to breed the mare, I asked the previous owner, he had not given them permission to breed the mare either. I moved all my horse from the property 3 days later, quitting my job there, telling the BO to stuff his boarding contract and sue me if he wanted to. I never heard from them again. Thankfully the mare turned out not to be bred, and eventually Whisper's mane and tail grew back, but it took over a year.
Some boarding stables can seem ideal on the surface, and do some REALLY shady things underneath. I will never have horses anywhere but my home - where I can watch them with my own two eyes, after my experience.