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Greasing the JointsBy Dr. Peter Huntington · March 29, 2011
Unlike their wild counterparts, domestic horses are asked to jump, to bend and flex into difficult movements, to stop and spin on a five-cent piece, to trot for hours or gallop at top speed around a track. All of this puts unnatural stresses and forces on their joints, pressures they were never designed to withstand.
Care of joints is critical to a horse realizing its athletic potential. For older arthritic horses, appropriate joint care may allow them to stay pain-free well into old age.
Numerous injectable and oral supplements are available for treating joint problems and maintaining the structural integrity and health of the joints. The injectable products are the gold standard as far as modification of joint health is concerned, but expense causes horse owners to look to daily oral supplements.
Why We Use Oral Joint Supplements
Joint supplements are used for both treatment and prevention of joint problems. Some owners feed joint supplements to a horse with existing joint injuries in an attempt to expedite recovery. Similarly, in the case of arthritis or severe injury, joint supplements can allow the horse to recover enough to become more comfortable. Others feed prophylactically, hoping to reduce the risk of injury from high-impact activities. Joint supplements are thought of as insurance against possible damage and are used in many top performance horses.
The Equine Joint
Any area where two bones meet within the horse's skeleton is a joint. The ends of the bones are coated with articular cartilage so they slide smoothly over one another during movement. Joints are encapsulated in a fluid-filled sac called the joint capsule that protects the joint.
The nutrient-rich synovial fluid that fills the joint capsule is an extremely slippery substance that allows smooth passage of one bone over another and absorbs some of the shock from high-impact work, where bones are forced together under great pressure. The fluid nourishes the articular cartilage with proteins, enzymes, and sodium hyaluronate, a glycosaminoglycan (GAG) that is an important structural component of joint cartilage and is responsible for the viscosity (thickness) of the synovial fluid.
Joint damage can involve any part of the joint or limb structure including tendons, ligaments, bones, articular cartilage, and the fibrous joint capsule. Damage to any of these components instigates inflammation, which allows large numbers of “cleanup” enzymes and prostaglandins into the joint. The GAGs are destroyed and the synovial fluid loses its viscosity. Without the rich nutrients of the synovial fluid, the articular cartilage starves and becomes damaged, giving way to bone damage as the bone ends begin to grind against one another. The bone responds by laying down more bone tissue, called spurs, which can further damage the joint and lead to severe joint inhibition and pain.
It takes more than a single traumatic strain or accident to cause this kind of damage. Progressive degeneration of joints is commonplace, especially in hard-working horses, and degenerative joint disease limits the careers of many performance horses.
Oral Joint Supplement Ingredients
Oral joint supplements generally contain a few key ingredients (glucosamine, chondroitin) that may be found alone or in various combinations. Supplements vary in price from reasonably economical to very expensive, and liquids are usually favored over powders. For a joint supplement to be effective, it must first be absorbed into the bloodstream, then it must travel through the circulatory system to the joints, and finally the body must be able to use it in repair of joint tissue. Products aim to counteract inflammation, reduce cartilage damage, and stimulate cartilage repair. Once each constituent has been investigated alone, the various combinations must also be researched as there may be some synergistic relationships, which suggest specific ratios of the various building blocks and their mode of delivery.
Research is extremely expensive, and the studies required to fully cover all the variables associated with equine joint supplements would take years to complete and cost millions of dollars. Investigating preventative aspects would also be very difficult. While we await these studies, we have only experience and anecdotal evidence to go on. What we can say is that most oral joint supplements will do no harm, as long as they don't contain prohibited substances. Because some supplementation can show benefits, a trial is often justified. Studies in the United States have shown great variation between label claim and actual composition in many products, so as well as comparing the contents, look for a label from a reputable supplement manufacturer.
Glucosamine
The most common ingredient in joint supplements is glucosamine. It is present in supplements either as glucosamine hydrochlorides or glucosamine sulphates. The former is a more concentrated and stable form of glucosamine, but they both seem to have similar biological effects. Glucosamine is an amino sugar that is the vital precursor to the synthesis of collagen and glycosaminoglycans (GAGs) in joint cartilage. Glucosamine can reduce GAG degradation and increase synthesis.
These GAGs include chondroitin sulphate (CS) and hyaluronic acid (HA), a major ingredient of synovial fluid and a key component of joint cartilage. GAGs are an essential part of the proteoglycans that make up articular cartilage. HA is an important contributor to the lubricating properties of joint fluid and elasticity as well as the shock-absorbing properties of joint cartilage. Glucosamine plays a vital role in reducing inflammation by inhibiting gene expression for destructive enzymes. It also scavenges free radicals that cause inflammation and pain and destroy the integrity of the cartilage matrix. The anti-inflammatory effect is a genuine modification of the disease process and doesn't act in an analgesic-only manner. Therefore, the end result is reduced pain and increased joint mobility.
Although glucosamine has low bioavailability in horses as measured by blood levels, it does accumulate in cartilage and is detectable in synovial fluid for at least 12 hours after dosing. Recent research has also shown that higher levels accumulate in inflamed joints than normal joints, and low concentrations of glucosamine can inhibit cartilage degradation.
When supplementing glucosamine, a dose of 10g per 500-kg (1100-lb) horse is now recommended and the beneficial effects may take at least four weeks to occur. Glucosamine is very safe, making it suitable for long-term use, although care should be taken in pregnant horses and those with insulin resistance or equine metabolic syndrome.
Chondroitin Sulphate
With respect to chondroitin sulfate (CS), absorption is debatable due to its large molecular weight (size) and varied molecular size used in joint-health products. CS is typically obtained from bovine, whale, or shark cartilage. Several studies have characterized the intact absorption as low, and bioavailability studies measure only the nonactive fraction of CS.
CS is the primary GAG that makes up the proteoglycans found in joint cartilage. It is known that joint injury and the ensuing inflammation cause a reduction in the amount of proteoglycans. Thus, CS theoretically could help replace proteoglycans. CS has also been proposed to inhibit the action of some enzymes associated with cartilage breakdown and to have general anti-inflammatory properties.
In vitro studies have shown some positive results with CS, and there are also some clinical studies with a combination of CS and glucosamine products that have been encouraging. One study in old horses showed increased stride length and range of joint motion, as well as improved soundness compared to control horses that were not treated. Definitive data to document the effect of CS are still unavailable, though the effects on gene expression seen with glucosamine were not observed with CS. CS-only products should supply 4.5g CS per 500-kg (1100-lb) horse, and it is recommended that CS is used in combination with glucosamine. In that situation a lower dose is appropriate.
