This person quotes an article from a horse magazine that has some useful advice for people who ride and have problems with their knees:
http://greyhorsematters.blogspot.co.uk/2009/11/riders-knee.html
I don't know how many of those tips you already follow, but I hope its useful, and helps...
I know Zylkene works really well for Dogs and Cats, but I haven't heard much about it for horses, though there is some information about it here:
http://www.msd-animal-health.co.uk/binaries/Zylkene_Client_Leaflet_tcm92-216000.pdf
At the risk of going against the general thread consensus, I am going to suggest eqvalan duo (http://www.viovet.co.uk/Non-Prescription_Medicines-Horses-Wormers-Eqvalan/c119_116_483_6253/category.html)
In terms of having all bases covered, you can't go wrong with it. Also, particularly at this...
Seraquin can also work well as a joint supplement for horses. At just over 65 pounds (that was the best price i found and was from viovet.co.uk), it is a lot cheaper than the synequin as well!
Hi,
I believe the tablets required are Prascend. As for the cost of them there is already a post which discusses the price of the tablets, should you need them:
http://www.horseandhound.co.uk/forums/showthread.php?t=536161
Hope that helps you :)