Originally Posted by kickshaw
i am unfamiliar with how to treat one whose stifles lock, but found this article, scanned it, and it seems that your vet is right: http://www.gaitsofgold.net/content/view/40/9/
It applies to gaited horses, but has great general information :)
Good luck and keep us posted!
Thanks so much for that! The article was very helpful with good tips on strengthening the stifles. I have decided to send Tommy to be started under saddle, with the idea that if he's broken to saddle I can commence the strengthening excersises. Lots of slow steady work will hopefully help, but at the same time it's important not to overdo it. It's a very fine line. Others have suggested to avoid circle work, which can put more stress on the stifles, which I will certainly avoid. It was a hard decision for me to send him to the trainer, but the concensus seems to be that work will improve it, and hopefully as he matures he will grow out of it.
PS Thankyou to everyone who answered my query, it's much appreciated, and has put my mind at ease.