Glucosamine and chondroitin sulfate are components of normal cartilage. They are both compounds already produced by the body, but production slows in the normal aging process (for both people & pets).
For use in dietary supplements, glucosamine is harvested from shellfish or can be manufactured/derived from a plant source (corn). It comes in different chemical forms, but the one most commonly used for arthritis and overall joint health is glucosamine sulfate. Effective joint support formulas usually contain Glucosamine along with MSM and Chondroitin.