I have a 16 year old thoroughbred who is an amazingshow horse (hunter/jumper).he constantly places over fences and on his hacks. but he had recently started losing his leads around the corners....no matter how much i push gis hunches in,he loses the lead or gets disunited in the hind legs. it isgetting worst quiclky.i am assuming its arthritis. he is on "dmac" supplement wich has shark cartillage,glucosamine and joint support vitamins in there.he also gets hock injections in the spring. Help!