Dr. Martin Adams, Equine Nutritionist for Southern States
There is a bewildering array of oral joint supplements available for horses. "How does this stuff work?', "Which ones work the best?" and "Are they safe for my horse?" are questions you may have asked yourself when reading about these products. While there is still much that we don't know about the effectiveness of these products, there has been some research to show that oral joint supplements can be used to treat lameness in horses. Following is a discussion of how oral joint supplements are classified, how they work, and which ingredients have been found to be effective in horses.
Oral joint supplements are classified as nutraceuticals. The term "nutraceutical" was coined to describe the increasing number of products offered for the prevention or treatment of disease or performance enhancement, but marketed as dietary supplements. The term "nutraceutical" combines the word "nutrient" (a nourishing food or food component) and the word "pharmaceutical" (a medical drug). Many of these substances are present in commercial equine feeds and common feedstuffs provided to horses. These include products that contain levels of essential nutrients beyond what is considered required for a particular species, as well as products that contain nutrients that are not recognized as being required.
A nutraceutical has been defined as "Any nontoxic food component that has scientifically proven health benefits, including disease treatment and prevention." The theory behind the mode of action of nutraceuticals is to increase the supply of natural building blocks in the body to provide a beneficial effect. Providing these building blocks can work to prevent or reduce signs of disease, or to improve athletic performance. There are a limited number of nutraceuticals whose effects have been researched in the horse. Regulation of nutraceuticals has not been resolved, there are no laws or regulations that define what a nutraceutical is, and federal guidelines for enforcement of safety or efficacy of nutraceuticals sold for equine use don't exist. Besides anecdotal evidence from horse owners of the effectiveness of these products, there is a lack of scientific data to support the claims for many nutraceuticals.
Oral joint supplements are not allowed in horse feeds because some of the ingredients in them are not on the list of ingredients that are "generally recognized as safe" (GRAS). Horse feed ingredients such as corn, oats, soybean meal, minerals, vitamins, flavorings, preservatives, etc. must be included on this GRAS list that is governed by the American Association of Feed Control Officials for legal inclusion into a horse feed.
Also, when a claim is made for a nutraceutical for the treatment or prevention of disease, it is subject to regulation as a drug. This requires demonstration of safety and efficacy for its intended use in order to meet Food and Drug Administration (FDA) approval, which is lacking for these products because of the expense. FDA's Center for Veterinary Medicine (CVM) is responsible for the regulation of animal drugs, medicated feeds, animal food additives, and devices for use in animals. Claims on animal feed products that have an intended use to cure, treat, prevent or mitigate disease are classified as drugs. Unless the product has been shown to be safe and effective for its intended use by controlled clinical studies it will not be approved for sale. In addition, any claims for the product to affect the structure or function of the animal's body may cause CVM to classify the supplement as a drug and prevent its sale because there is a lack of safety and efficacy information.
Joint lameness resulting from athletic performance in horses is a common problem. The horse's joint has two means of protection from the mechanical stresses from physical activity, synovial fluid and articular cartilage. Oral joint supplements contain ingredients to replace or manufacture these two substances. Obviously, for joint supplements to be effective, the substance must be absorbed into the horse's bloodstream, transported into the joint capsule, and utilized for repair or replacement functions. The main ingredients used in oral joint supplements are sodium hyaluronate, glucosamine sulfate, glucosamine hydrochloride, and chondroitin sulfate. Oral joint supplements are available in powdered, pelleted, liquid, and gel forms. Other ingredients that are commonly included in oral joint supplements include MSM (methylsulfonylmethane), copper, zinc, manganese, and vitamin C. MSM is a bioavailable form of sulfur, which is a component of collagen. The trace minerals copper, zinc and manganese are required cofactors for enzymes involved in cartilage metabolism. Vitamin C or ascorbic acid is a component of hydroxyproline, an amino acid that is a major component of collagen.
Synovial fluid, which provides lubrication for ease of movement in the horse's joints, contains proteins, enzymes, water, leukocytes, and sodium hyaluronate. Sodium hyaluronate or hyaluronic acid is a low molecular weight glycosaminoglycan (GAG) composed of glucuronic acid and N-acetylglucosamine. Sodium hyaluronate functions as a lubricant and shock absorber in the joint. Intra-articular, intravenous and intra-muscular injections of sodium hyaluronate have been used to effectively treat joint disease in the horse. Addition of sodium hyaluronate by these methods increases viscosity of synovial fluid, inhibits cartilage-damaging enzymes, and promotes production of sodium hyaluronate. Oral sodium hyaluronate is poorly absorbed in humans, and there is no data on intestinal absorption of sodium hyaluronate in horses. Oral sodium hyaluronate products for horses are commercially available, and anecdotal evidence suggests similar effects for treatment of lameness and joint disease as injectable products after two to three weeks of daily administration.
Glucosamine is included in oral joint supplements either as glucosamine sulfate or glucosamine hydrochloride. Cartilage is composed of collagen fibers containing chondrocytes. Chondrocytes synthesize glucosamine, which is a precursor of sodium hyaluronate and the disaccharide unit of GAG, which comprises the proteoglycan found in articular cartilage. Inflammation of a joint from physical stress results in excess fluids, destructive enzymes and prostaglandins in the joint capsule. This results in loss of lubricating GAG molecules and lowered viscosity of synovial fluid. Proteoglycan synthesis by chondrocytes decreases, which lowers cartilage repair rate. Absorption of glucosamine hydrochloride following oral administration has been demonstrated in the horse. There is no available research literature documenting absorption of glucosamine sulfate in horses after oral dosing, but there is a large amount of evidence documenting effective absorption in man and dogs. In vitro data with equine cartilage supports the concept that glucosamine hydrochloride is effective at stimulating cartilage synthesis and inhibiting prostaglandin release. However, there are no published equine studies showing the effectiveness of glucosamine hydrochloride or glucosamine sulfate for treatment of lameness or arthritis.
Lameness can result from damage to any of the tissues associated with the joint, which results in a change in the normal range of motion. Damage to the articular cartilage such as breakdown of collagen or loss of proteoglycan can result in weakened cartilage. This weakened cartilage can develop cracks that disrupt its smooth articulating surface, resulting in lameness. Chondroitin sulfate is the most abundant GAG present in articular cartilage. Since it is known that joint injury leading to inflammation causes a reduction in the amount of proteoglycan, replacement of chondroitin sulfate could replace proteoglycan and restore articular cartilage to a normal state. Chondroitin sulfate has also been proposed to have anti-inflammatory properties and inhibit destructive enzymes associated with cartilage breakdown. Data to support these proposed actions of chondroitin sulfate from an equine in vitro study has shown positive results. Although molecular weight of chondroitin sulfate is greater than glucosamine products, bioavailability of low molecular weight chondroitin sulfate has been documented in horses after oral administration. Chondroitin sulfate is an effective oral joint supplement. Oral administration of chondroitin sulfate significantly reduced lameness scores over controls for horses induced with aseptic arthritis.
There is evidence that an oral joint supplement with a combination of chondroitin sulfate and glucosamine hydrochloride is more effective than a product with chondroitin sulfate alone. In vitro studies using equine cartilage have shown that a combination of glucosamine hydrochloride and chondroitin sulfate had a synergistic effect on stimulation of cartilage synthesis and protection from degradation. Significant improvement in lameness scores were observed for horses provided with a powdered oral joint supplement containing chondroitin sulfate and glucosamine hydrochloride. Combination products with chondroitin sulfate and glucosamine sulfate are also effective in reducing lameness.
There is increasing evidence that oral joint supplements are safe and effective for horses. Consider a joint supplement that is a combination product, containing chondroitin sulfate in addition to glucosamine sulfate or glucosamine hydrochloride. There are also chondroitin/glucosamine products available that contain sodium hyaluronate, these would be good choices also. The addition of copper, zinc, manganese, vitamin C, and MSM is common in these products and would be beneficial to insure that all essential nutrients for cartilage and synovial fluid production are in sufficient concentrations. These oral joint supplements will allow you to keep your horse moving "smoothly".