Please use this to learn a valuable lesson. Ask a lawyer to write up a contract next time. Your contract says nothing about the horse's body condition, feeding, immunizations, worming, water access,
Your contract doesn't say who they have to let do this horse's hooves. Heck, you might have difficulty defending that in court as many horses don't get their hooves done and, if a horse develops some hoof disorders, shoes might save a horse's life. Your contract says the horse cannot have shoes.
I'm not a lawyer either but I'd bet that your contract contains some unenforceable items and leaves out an awful lot of important things.
The thing is this...it does not appear that they even have to let you visit this horse. If you're not nice to them they may not allow you to visit this horse or know a thing about its condition.
Are you absolutely sure you wanna mess with my carrots?