When I first got my mare 2 years or so ago, she was out of shape (for an Arab mix) and had really bad tendon issues from her former barrel racing owners not warming her up before a race. She could barely walk 5 years ago. The ranch that I work at acquired her as a donation before I started working there. A year ago, once I was able to get some money, I started her on a daily dosage of RapidFlex, which you can get in most feed stores and some WalMarts. It's about $40 for about a 40-60 day dosage (I can't remember offhand which). We'd previously had her on GlucoFlex, which is more expensive, with limited results. RapidFlex works like a dream! My mare is ridden regularly, handles hot Arizona summers, and can ride through sand dunes and the like now at the age of about 18. If you have a horse who has tendon issues, RapidFlex is a great go-to product before you try injections or the more expensive treatments.
We feed RapidFlex with about 2 cups of soaked red bran and a tablespoon or so each of diced garlic, vegetable oil, and apple cider vinegar, as well as a scoop each (included with the product) of electrolytes and MSM. We've added RapidFlex to our older 25-27 year old arthritic gelding's feed, as well as a smaller dosage to an older mini. They're all doing so much better. Definitely worth a try!