I've done a lot of research on oral supplements, taken some seminars from equine nutritions, and there are some good ones out there, Exceed 6-way, and Pureform Gluclosamine Plus are ok. My personal preference is Recovery. With a barrel horse I'm not only worried about joints, but tendons, ligaments, respiratory, etc. and Recovery covers all of that
10000mg gluclosamine - joints
10000 mg MSM - inflammation and pain
1000mg TMG - which the horse converts in to DMG, a substance the horse produces themselves, but increased doses help with respiration and recovery, DMG is widely used on racetracks and with "heavey" horses
1400mg buffered vitamin c - buffered c will not upset the horses stomach like pure ascorbic acid vitamin C. Horses produce their own vitamin C, but as they age their ability to produce it decreases, and vitamin C is essential to feed the collagen in healthy joint fluid and tissues in tendons/ligaments.
750 IU Vitamin E - a potent antioxidant and anti inflammatory
1000mg Nutricol, which is a combination of Grape Seed Extract and Green Tea. The manufacturer told me there is about 750 mg of GSE and 250 of Green Tea - GSE has been researched to widely improve cardiovascular and gastric health in horses.
I have priced out purchasing all these items seperately thinking I may save money - but it is cheaper to buy Recovery and have 1 bottle instead of 7! It also comes with HA for improved gluclosamine absorption.
Pureform doesnt' have any grape seed extract - and to feed it seperately is about $2 a day... it also has ascorbic acid vitamin c - which can upset the horses stomach lining. Exceed 6-way contains Yucca, which you need to be careful in horses that already have joint issues, it can increase inflammation in some horses.