We have several horses with major joint problems and we give then hyaluronic acid and MSM on a regular basis. We also use hyaluronic acid cream on the affected joints. Basically hyaluronic acid is the most important and MSM reduces the discomfort.
Hyaluronic acid helps maintain cartilage and MSM helps with the pain and inflammation that goes along with joint damage. But the key is taking them for a long time. Our vet said that we probably have to give these supplements forever for the horses with injuries for them to get the most benefit.