There is a huge range of joint supplements on the market, and they vary a great deal in quality and contents, but the aim is simply to provide joint specific nutrition to maximise maintenance and repair, thus prolonging the life of the joint and helping to prevent lameness. If you have ever looked at some joint supplement labels you will have seen a variety of ingredients, while most are for nutrition you may also see other natural ingredients which reputedly reduce pain or inflammation.
Most fundamental nutrients are associated with a family of compounds known as glucosaminoglycans, or GAGs, which form a large part of the joint and connective tissue structure. They also bind with water making them resistant to pressure, which is vital to allow the joint to transfer pressure for efficient movement, whilst absorbing impact to prevent damage.
Glucosamine is the most common ingredient, it is highly abundant and easily sourced and refined, commonly from the shells of crustaceans. Increasing glucosamine intake allows the body to make various GAG compounds needed for joint function.
Some supplements will include GAGs in their complete form. The most common of such ingredients is chondroitin, which is a component of joint cartilage and may also be involved with allowing nutrient transfer. HA (hyaluronic acid) is another which vets often inject directly into the joint. It is a vital component of synovial fluid and is also thought to help prevent cartilage degradation caused by certain enzymes, but the benefit you get from oral supplementation is highly questionable as the amount that can be absorbed may be very low.
You may also see an array of holistic ingredients. Large claims are often made about various herbal remedies, but some caution is required because the knowledge of how, and even if, these remedies work is extremely limited and there is little scientific evidence in their support. Also be aware that with pain killing remedies such as Devils Claw, you could be masking symptoms without improving repair, thus allowing the joint to deteriorate further.