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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.

Methylsulfonylmethane (MSM) and Methionine

Methionine, a sulphur-bearing amino acid, is converted to an important component of connective tissue, S-adenosylmethionine, which has been used successfully in clinical applications in humans for the treatment of osteoarthritis. Unfortunately, S-adenosylmethionine is expensive, but its precursors are not. Methionine is a sulphur-bearing amino acid that acts as a catalyst and aids in the metabolism of glucosamine to glycosaminoglycan (GAG). The sulphur supplied by methionine is also used in the synthesis of collagen, which gives strength to connective tissue and cartilage. MSM is a source of organic sulphur and is thought to have anti-inflammatory effects. However, there are no data to substantiate how much MSM is required for this effect, or if MSM provides a protective effect on cartilage.

Trace Minerals (Copper, Zinc, Manganese)

Zinc is required for the functioning of over 70 different enzymes within the horse. For joints, it is essential for hydrolysis and cross-linking needed for collagen formation. Zinc-deficient animals have been shown to have impaired cartilage and collagen development. Copper is a coenzyme required for the formation of the disulfide bonds in collagen that are needed for strength and elasticity. Manganese is important in this formula as a cofactor in GAG and hyaluronic acid(HA) synthesis, and in cartilage repair and maintenance.  It is also involved as a cofactor in collagen formation. Most unsupplemented home-mixed diets will not contain enough zinc, copper, or manganese to supply the needs of athletic horses.

Antioxidants

Vitamin C is a powerful free-radical scavenger. Free radical levels are higher in inflamed joints and can damage collagen and proteoglycan(PG). Vitamin C plays several roles in the formation and maturation of collagen, but again there are no data on horses on the value of vitamin C in a joint supplement.

Omega-3 Fatty Acids

Research in humans and many animals has shown that long-chain omega-3 fatty acids EPA and DHA have an anti-inflammatory effect that can benefit joints as well as other parts of the body. Many humans take fish oil supplements to reduce inflammation and pain in joints, and recent research has found similar effects in horses. Supplementing EPA and DHA in fish oil led to reduced markers of inflammation in the joints of both yearlings and older horses with arthritis. Another study found increased trot stride length in horses given EPA and DHA, and this was thought to relate to reduced joint pain. Performance horses are the perfect candidates for omega-3 supplementation as they are often fed large amounts of grain, which normally contains an abundance of omega-6 fatty acids, to maintain body condition. There are many reasons to supplement long-chain omega-3 fatty acids, but care of the joints is an important consideration.

Hyaluronic Acid

Hyaluronic acid (HA) is a naturally occurring substance in the joint and other connective tissues.  It is produced by the synovial membrane lining the joint, and is the primary agent responsible for the viscosity and lubricating properties of the synovial fluid. It is also a regulator of cell and tissue function and has cell-signaling (anti-inflammatory) properties. HA is the backbone of aggregate PGs in articular cartilage and contributes to cartilage structure. It also has some antioxidant properties.

There is regular turnover of HA in the joint, and research has shown that horses produce 30-160 mg of HA per day, which is incorporated into synovial fluid and cartilage. However, inflammation resulting from exercise leads to a hastening of the breakdown of HA, which in turn causes reduced joint fluid viscosity and a vicious cycle of further inflammation. HA has a very short half life in horses, especially after intravenous injection, after which blood levels have been shown to return to normal within three hours. This rapid clearance of HA from intravenous delivery suggests that regular daily oral administration will be useful.

The size of the HA molecule is measured in units called Daltons. Natural HA has a molecular weight of 1 million Daltons or more, and studies have shown that low-molecular-weight HA material does not have the same properties as natural or supplementary high-molecular-weight HA.

Due to the size of the molecule, absorption of HA is a considerably variable. The other issue is how absorption into the blood, or more importantly the joint, is measured. Oral dosing of radioactively labelled HA of 1 million Daltons in size has shown that there is uptake of HA into the joints of rats and dogs for up to 48 hours after a single dose.

Oral supplements are easier to use and less expensive than intravenous (IV) or intra-articular (IA) treatments. Given the rapid clearance of HA from the blood and synovial fluid after IV or IA administration, daily oral supplementation can be used to augment IV or IA treatment and maintain concentrations of HA in the joints. 

Shark Cartilage, Green-Lipped Mussel, and Sea Cucumbers?

Are substances extracted from the sea useful for joint health of horses? Shark or bovine cartilage and perna mussels are natural sources of chondroitin sulphate, but there are concerns about how much CS these sources contain and the ability of the horse to absorb CS, especially from an unprocessed source.

Green-lipped mussel extract is included in many joint supplements because it is thought to contain various beneficial substances including glucosamine, CS, proteins, minerals, and omega-3 fatty acids. Although there has been some research done on rats that showed anti-inflammatory effects, there is no equine research available and bioavailability of the nutrients within the extract is unknown.

The bottom line regarding the efficacy of oral joint supplements is still unclear. Many knowledgeable horsemen have used joint supplements on horses in their care with great success, but others have tried supplements and reported no detectable differences. If used for preventive purposes, how can you tell if they are valuable? Well-designed clinical trials conducted by reputable companies using large numbers of horses are needed to validate efficacy and value of these products. Many potentially valuable benefits of oral joint supplements exist, but to date the efficacy of these supplements in horses is still unproven and many products do not contain enough of the key ingredients. The good news is that some controlled research is being conducted to answer important questions surrounding oral joint supplements.