I've come across alot of heavily used performance horses with shot joints that have had it injected in the joint, but none that were fed it orally. When my big paint colt came up with OCD, the vet wanted to shoot his hocks up with it, and I ventured out for a 2nd opinion. Opinion was that it is injected into the joint to lubricate it and should be used as a last resort as it will eventually cause the joint to break down even further. I would think that feeding it orally doesn't allow the horse's body to naturally produce the needed lubricant like glucosamine/chrondroitin suppliments or thiamine does, as it is used as a lubricant itself.
So, we elected to do nothing on the colt and his chipped hocks, and he's never taken a lame step in his life. He's now 6. I doubt he could hold up for heavy performance for any length of time, but for western pleasure and trail riding, he's as sound as can be. Now, for the advice part.......I had an old gelding who popped his knee joint out in 97. Basically the joint capsule was compromised and osteoarthritis was a basic fact of his life. He had very limited range of motion in that knee, and as a result, I don't think he layed down for the first 2 years after his injury. I found the need to put the paint colt on a hoof suppliment as his feet are very brittle, so I found a product called "Bio Plus". I chose this product because it packed the most biotin for the least amount of $$. What I found was that it didn't do a darned thing for the colt's feet, but after about 3 months on the product, the old gelding was able to bend his knee enough to lay down again. So, for 5 years after that, I religiously used the product for the old gelding. I would notice him favoring the knee if I ran out and he had to go for a week without it, so I know that stuff was the reason he was out of pain. It contains the biotin, and yucca, and Sulfer and someother stuff. Whatever it has in it, it worked on the osteoarthritis, and I swear by it. It worked when the Adequine injections didn't, it worked when the glucosamine/chondriotin suppliments didn't, and it worked when straight MSM didn't. My thoughts are that its worth a try for the $100 or so for 3 mos of supplimentation it would take to get it into his system, and it will leave you room to go to something stronger if the situation warrants it. I think I found it at
http://www.Americanlivestock.com, or jeffers or somewhere like that. Whatever it did or has in it, it was the right combination of stuff to allow my old guy to live pain free, and that was what mattered.
Keep us posted on what you decide, and what the results are!