I had a long post typed out, but then decided it was TMI.
Shorter post: I know you’re on the west coast, but it might be worthwhile having the horse checked for lyme disease. There is lyme on the west coast, but I’m guessing that vets don’t see it often enough for it to be a regular topic of conversation anytime a horse presents as lame or slightly off. At the very least it’s worth talking to the vet about.
I did have good results with oral HA, better results than I had with adequan or Legend. But, that was with my one horse, much of whose arthritis may have been attributable to lyme disease (although it’s impossible to know for sure). When she had an active case of lyme, the doxy definitely helped. YMMV.
Supplements for the most part are not going to have the classic double-blind clinical trials to prove efficacy because there are not a lot of companies who are willing to fork over the research dollars to run those trials. My advice is to try them for a month or so and see if you see any difference in your horse.
That said, I never had much in the way of results from either Cosequin or Corta-Flx, both of which do have (limited) clinical trials to support their claims.
When all else seems to fail, there’s always Dr. Green. Pull the shoes and turn-out with very little stabling for a few months and see what you have at that point.
