Truthfully, I think the best bang for your buck is Adequan or Pentosan (intramuscular injection) if you want something as more of a preventive. They are thought to be better than a feed-through because it's really unknown how much of a feed-through supplement maker it through the Digestive system and makes it to the joints.
With that said, I do still feed a feed through supplement. Platinum performance CJ is a great one. I currently feed T.H. E. Muscle mass with custom joint support blend. My horses respond better to it.
Keep in mind that ANY supplement is trial and error. One persons horse will respond to something and another person's won't.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.