In order for a horse to have healthy bones and joints, there are four minerals and two vitamins that must be in adequate supply: calcium, magnesium, boron, copper, and Vitamin A and D. Reducing grain and alfalfa, and increasing quality oat and grass hay is the first step. Find an equine nutritionist to help you come up with the optimum balance. Many horses crippled with arthritis can be improved to the point of going back to their disciplines when an imbalance is corrected.
There was a famous steeple chase horse named Babble Boy, who at age 31 was unable to move from his paddock. He was put on boron, unlimited seaweed feed, salt, apple cider vinegar, and copper, cod liver oil, and in less than two weeks could trot comfortably.