IT IS estimated that oral joint supplements account for around one-third of all equine supplement sales.

Their popularity bears testament to the fact that joint diseases, and especially osteoarthritis, are common in horses and have no definitive cure.

While there is lots of anecdotal evidence that joint supplements are effective in both in preventing osteoarthritis and treating its signs, few controlled clinical trials have been undertaken. But how do these supplements work and what do recent studies tell us?

Joints are structured so that the load bearing ends of bones are coated with a thin layer of well lubricated, friction-reducing cartilage, which allows normal and pain-free movement.

Injury to a joint results in inflammation. With its accompanying pain, this is designed to protect the joint by restricting movement, breaking down damaged tissue and allowing healing.

Inflammation also, however, has unwanted effects of disrupting normal joint lubrication and accelerating wear of the joint surfaces. This results in loss of articular cartilage, exposure of underlying bone and new bone formation at the margins of the joint. These are cardinal features of osteoarthritis.

The main aim in treat degenerative joint disease is to reduce inflammation. This has traditionally be done using a combination of physical therapies – such as rest, application of heat or cold, bandaging, and controlled exercise – and anti-inflammatory drugs like 'bute'.

Newer anti-inflammatory medicines such as hyaluronic acid (eg Hyonate) and polysulphated glycosaminoglycans (Adequan), which are injected directly into joints as well as into muscle or veins, have the potential to also improve lubrication, repair cartilage and protect it against further destruction. It is these same advantages that are offered by some constituents of oral joint supplements.

Joint supplements contain one or more nutraceuticals. These are defined as dietary components that provide health benefits beyond their traditional nutritive value. The most common neutraceuticals in joint products are glucosamine and chondroitin sulphate. Others are polyunsaturated fatty acids, antioxidants and micronutrients like zinc, copper, manganese and methylsulphonylmethane (MSM).

Glucosamine and chondroitin sulphate are essential building blocks for cartilage and the body has some ability to produce them itself. Oral supplementation, however, augments this reserve capacity with the potential of both increasing production of articular cartilage and inhibiting its destruction. This will reverse the effects of inflammation and preserve the health of a joint.

Beneficial effects glucosamine and chondroitin sulphate on articular cartilage have been observed in laboratory studies using tissue cultures that mimic both normal and inflamed joints. Furthermore there is evidence that the two nutraceuticals may work together to produce greater effects and there have been two clinical trials looking at their combined effects.

In the first, gait characteristics were assessed in older horses given either supplement or placebo. This was a controlled study in which the investigators were 'blinded' to what the horses received. After 12 weeks horses on the supplement had significantly better range of movement in several joints, including the elbow, stifle and hind fetlock, and greater stride length.

The second study, on horses with moderate osteoarthritis, found that overall lameness and pain on manipulation of affected joints was reduced by approximately a third over a four-month period. Greater improvements were seen in horses given undenatured type-II collagen, which is a neutraceutical harvested from the soft sternum of chicken carcases.

But joint supplements are not without their sceptics, especially among some vets and scientists who point out that less than 5% of glucosamine and chondroitin consumed is actually absorbed into the body. This, they argue, makes it difficult to reproduce in the body levels used in laboratory studies where benefits have been recorded.

Recent research has, however, countered this by providing evidence that much greater concentrations of glucosamine are found in inflamed joints. These levels are, in fact, not dissimilar to those where benefits have been recorded in laboratory studies.

Other questions that need to be addressed include what are the best sources and most appropriate oral doses of glucosamine and chondroitin sulphate, as this will to a large extent help answer the question which supplement is best.

Polyunsaturated fatty acids, antioxidants and other micronutrients are believed to play a role in reducing inflammation and supporting growth or repair of cartilage.

Controlled studies of joint supplements in preventing onset of osteoarthritis would also help address the question of whether, if fed from an early age, they can prevent or delay the onset of lameness later in life.

In this respect it could be said that joint supplements are much like anti-ageing creams: they are costly and you won't know if they work until it's too late!