Greasing the Joints, Part Two: Oral Joint Supplement Ingredients

This article is a continuation of Greasing the Joints, and further investigates some of the important ingredients found in oral joint supplements for horses and what they can do for your horse.

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.