Heard the same thing here. My vet just doesn't see how the oral supplements can truly cross over the way they would need to. My 8 year old OTTB mare is just finishing up the loading dose of Adequan, she will then get 3 doses of Legend and will be on a 1x/month Adequan schedule. So far she runs and bucks MUCH more then she used to and the other thing I have noticed is I used to have to put standing wraps on the horse because she would blow up like a balloon in her stall every night, since starting her on the Adequan she no longer stocks up and I have not been wrapping her, so it IS making a difference. While it is costly for the loading dose, it only runs aprox $40/month to keep up on 1x/monthly Adequan injections which is less what most good oral joint supplements run anyway. I do however still give her supplemental MSM.
BTW I noticed that you said it was an OTTB and he was between 6-10, if you flip his lip and tell me the letter that his tattoo starts with I can tell you eactly how old he is.