^this what Dancing said. Many times supplements won't work because the joint damage has gone BEYOND maintenance. Many of these feed throughs do nothing, if it's gone beyond a certain point...and all you are doing is feeding something that is not going to be utilized by the body. And many times, for the supplement to be effective...you have to feed MUCH more than what the label calls for. Many vets say that the feed throughs are a waste of money depending on what the horse actually needs. The best one really is Cosequin and it's pricey. The best route to take...is to get yoour vet out, assess the actual health of the horse's joints to begin with...otherwise, you could be wasting your money big time.
It's true that glucosamine doesn't really work if ALL the cartilage is gone. However, that type of damage is pretty extensive, and it takes a long time for joints to get that bad. The best idea is to start supportive measures when stiffness is first noted before it gets THAT bad.
There are injectable forms of glucosamine (as well as hyaluronic acid) that REALLY do work. Adequan is an example. It just plain works! And, in my experience, it works better than cosequin. I gave cosequin to my dog for years, but when she got BAD and the cosequin no longer helped her, we switched to adequan and WHAM she was dancing like a puppy! Adequan is also made for equines.
My gelding showed great improvement with next level. I just watched him for a month to see how he was acting and sure enough, he was romping around kicking up his heels etc! I was grateful! I decided to try feed throughs first before paying for expensive xrays. I guess just because of my modest budget, I'll try what I can first before opting for more expensive stuff. And for my gelding, it works! YAY!