I don't know about the Synov, but I swear by the Cosequin! My cocker was only about 7 when she started showing signs of arthritis. The vet put her on a daily dose of Cosequin, and we noticed a huge improvment within a year. My parents decided to take her off the drug, just to see how she would do. She was great - it's as if that year of being on cosequin cured her of her arthritis forever (well, until she was 12 or 13, at least!).