You notice that your competition horse is starting to shorten his stride occasionally. He is stiff and takes longer to warm up. Perhaps he's showing other signs of physical discomfort. Your veterinarian examines him, and the result is what you expected--he is developing arthritis. Now what? Should you start him on a joint supplement of some type? You know that every time you open a horse supply catalogue, there are pages of advertisements devoted to oral joint supplements. What are all those ingredients, how do they work, and (most importantly) do they work at all? That last question is the big one, and the jury is still out.
What Is Cartilage?
Cartilage is a resilient tissue covering and cushioning the joint surfaces of bones. The cartilage matrix is made up of collagen fibers, glycosaminoglycans (GAGs, natural joint lubricants), and sodium hyaluronate. Both cartilage and joint fluid act as shock absorbers and buffers to keep bones from rubbing together (see the illustration on page 86).
Cartilage doesn't have its own blood supply; it must rely on surrounding tissue for its nutrients. When cartilage can no longer maintain proper metabolic activity, the destructive processes begin. This happens with normal aging and physical wear and tear, and the end result is that the joints become less flexible.
Many joint supplements claim to improve or maintain cartilage health.
What Are the Choices?
There is a wide variety of ingredients in oral joint supplements, but many contain chondroitin sulfate and/or glucosamine. They are meant to support joint health by slowing the cartilage degeneration process and decreasing discomfort and pain through anti-inflammatory effects.
Chondroitin sulfate--This is one of the primary GAGs in joint cartilage. It is produced in the cartilage by chondrocytes and is believed to act as an anti-inflammatory agent and inhibit some enzymes that hasten cartilage breakdown. Oral chondroitin sulfate has been shown to have some anti-inflammatory effects in humans, but this has not yet been demonstrated in horses, and there is a question as to its rate of absorption. The supplemental ingredients are comprised of cartilage, skin, vertebral disc, and other tissues obtained from slaughtered cattle trachea, shark cartilage, and sea mussels, but it is not known if the source makes any difference.
Glucosamine--Glucosamine is a complex sugar molecule from which proteoglycans are made. It is a building block of chondroitin sulfate and helps give synovial fluid its resilience and elasticity. In addition, it stimulates the production of GAGs by joint cartilage and increases the utilization rate of chondroitin sulfate. The glucosamine molecule is smaller and simpler than chondroitin, thus it is thought to be more easily absorbed. In humans, it has been shown to be an anti-inflammatory pain reliever and absorbed from the gastrointestinal tract. Glucosamine is extracted from chitin, which is found in the shells of shrimp and crabs.
Methylsulfonylmethane (MSM)--This white, tasteless, odorless, crystalline powder has probably been the nutraceutical used for the longest period of time. It's an organic compound derived from DMSO (dimethyl sulfoxide, a topical gel or liquid that is used in horses to reduce swelling from trauma), and it appears naturally in small amounts in the bloodstream as well as in milk, vegetables, fruits, and grains. It provides a source of bioavailable sulfur, which is necessary to form connective tissue.
Other products--In addition to the substances described above, you might see manganese added to joint supplements. This mineral is thought to help activate the enzymes needed to make GAGs.
Yucca and devil's claw, two other common ingredients, are herbal anti-inflammatories (although there can be complications with abuse of natural products, too).
Finally, some of the newest products on the market are oral gel products containing hyaluronic acid. David Ramey, DVM, a private practitioner focused on performance horses, is very skeptical of these.
"Hyaluronic acid would be expected to be digested in the intestinal tract," Ramey says. "Then, even if it were absorbed, it would be almost immediately removed by the liver. It has a half-life, measured in a couple of other species, of about four minutes."
Oral Supplement Issues
The number of oral supplements available seems to be growing by the day. They come in many forms, including powder, pellet, liquid, and gel. These supplements are called "nutraceuticals," a term borrowed from the human industry. It refers to products that are neither feed nor drugs, but considered somewhere in between the two. It is important to note that only a drug can make a medical claim (treat or cure a problem). In contrast, these products are marketed as nutritional supplements with implied medical benefits.
Nutraceuticals are comprised of non-toxic food components that are sprinkled or poured on feed or given as pills or paste. Because they are not designated as drugs, they can be purchased without a veterinary prescription. The North American Veterinary Nutraceutical Council describes nutraceuticals as substances "produced in a purified or extracted form and administered orally to patients to provide agents required for normal body structure and function, administered with the intent of improving the health and well-being of animals."
Unfortunately, there are many unanswered questions regarding nutraceuticals. One is whether or not they contain what the label states. The University of Maryland tested 27 glucosamine or chondroitin sulfate products in one study; a number of them didn't contain the amounts that were listed on the label. In addition, the amounts could even vary from month to month.
Unfortunately for the consumer, the product names used in this study were not released. Keep in mind that manufacturers are not required by law to guarantee the amount of each ingredient or describe the product's action. Furthermore, "effective" dosage levels of these substances have not been determined in horses. In other words, there are no guarantees whatsoever of ingredient levels or efficacy in horses.
Many theories behind joint supplement use in horses were established first in humans. However, an ingredient that is approved to sell for human use isn't necessarily approved to sell for animal use. Wayne McIlwraith, BVSc, PhD, FRCVS, DSc, Dr. med vet (hc), Dipl. ACVS, Director of Orthopaedic Research at the College of Veterinary Medicine and Biomedical Sciences at Colorado State University,
recently published a review that contained information about nutraceuticals. He presented the information at the 50th Annual Convention of the American Association of Equine Practitioners (AAEP) held in December 2004 (see www.TheHorse.com/ViewArticle.aspx?id=5582).
McIlwraith says, "Many nutraceuticals or nutritional supplements marketed for the horse are illegal because the manufacturer has not complied with FDA ingredient-recognition processes, not completed ingredient-definition applications as described by the Association of American Feed Control Officials (AAFCO), not followed state licensing requirements, and/or made false claims on the product label."
Medical products fall under the FDA and must undergo rigorous testing, be properly labeled, and show effectiveness. Nutritional products do not need to meet these same requirements.
Ramey states that right now, U.S. laws make it exceedingly difficult for any regulatory agencies to get involved. Companies often use unsupported, vague claims that are outside the regulatory arena. Since the FDA pays little attention to the equine nutraceutical market, there is no incentive for a manufacturer to get a license.
In an effort to help promote proper practices by manufacturers and standardize the animal supplement industry, the National Animal Supplement Council (NASC) recently initiated a Quality Seal Program. This seal lets consumers know they are buying from a reputable manufacturer that has gone through an independent audit and has implemented specific standards and conformed to quality system requirements. As reported by The Horse (see www.TheHorse.com/ViewArticle.aspx?id=5287), the following criteria are necessary before being able to display the seal:
- The company must have a quality manual in place that provides written standard operating procedures for production process control.
- The company must have an adverse event reporting/complaint system in place to continually monitor and evaluate products.
- The company must follow proper label guidelines for all products.
- The company must include any specific warning and cautionary statements recommended by the FDA's Center for Veterinary Medicine and the NASC Scientific Advisory Committee.
What the Research Shows
McIlwraith states that to prove efficacy of a substance, you need either a controlled experimental study with consistent levels of disease or a double blind controlled study with appropriate numbers. Researchers need a large enough sample for reliable statistics. Randomized, controlled, and blinded clinical trials are difficult and expensive in horses, and observational, descriptive, and anecdotal studies do not prove efficacy. Furthermore, bioavailability and absorption studies are useful as pilot studies, but again they do not show efficacy of treating or preventing disease in animals.
One of the oldest joint supplements on the market is Cosequin, which contains low molecular weight chondroitin sulfate, glucosamine hydrochloride, and manganese ascorbate. McIlwraith commented that this company was one of the few that actually had conducted research on its product, and that other companies have often "borrowed" that data and applied it to their own products, which might or might not have the same ingredients.
Available on the company's website (www.cosequin.com) are the results of five studies that showed positive effects of Cosequin. The studies using live horses found that Cosequin supplementation was safe and effective, but the number of horses used in these studies was small. In addition, one study was not blinded or controlled. They also have in vitro studies that suggested the combination of glucosamine and chondroitin sulfate complemented one another and was more beneficial than either compound alone.
In a separate study, Hilary M. Clayton, BVMS, PhD, MRCVS, of the Mary Anne McPhail Equine Performance Center at Michigan State University, used the product Corta-Flx to see what effect it had in horses with tarsal (hock) problems. A double-blind placebo-controlled design was used with 10 subjects, and the results were published in the 2002 AAEP Proceedings.
"The results clearly indicated that treatment with Corta-Flx for two weeks produced a more symmetrical gait pattern, which was interpreted as being indicative of an improvement in locomotor function," Clayton said. "It is unrealistic to expect that an oral supplement of this type will restore complete soundness, but an effective product might be expected to improve the lameness so that the horse's gait pattern more closely approaches left-right symmetry...It is concluded that the gait pattern at the trot became more symmetrical in horses with degenerative joint disease after treatment for two weeks with Corta-Flx, an oral supplement designed to aid joint health."
McIlwraith described additional studies, including one in horses, that showed chondroitin sulfate (of the same low molecular weight as Cosequin) was absorbed into the system. Evidence of oral absorption of chondroitin sulfate has been shown in the horse, as has absorption of glucosamine, but the amount is low. One study showed the absorption rates from glucosamine administered through a nasogastric tube is lower that what has been found in in vitro (outside the body) studies. McIlwraith also summarized several studies that showed no detrimental effects of glucosamine or chondroitin sulfate on cartilage metabolism, and that intermediate doses enhanced GAG synthesis and content.
The Bottom Line
Ramey feels that it is unfortunate that people spend a great deal of money on products that have, as he says:
- Variable purity;
- Little to no evidence of efficacy; and
- An implausible mechanism of action.
McIlwraith concluded, "It is to be emphasized that when equine veterinarians use licensed medications, the patient gets the best care in that an accurate diagnosis is made. It is an unfortunate reality that many instances of lameness and joint disease are presented after client-prescribed periods of oral nutraceuticals have failed to yield results."
Still, there are many people who believe these oral supplements are helping their horses, and maybe they are. However, until there are scientific, repeatable studies done utilizing large numbers of animals, horse owners really don't know to what extent these products are effective. The best course of action is to talk to your veterinarian about a complete treatment regime.
Arthritis is a problem, but often a manageable one. A combination of management practices, which might include oral joint supplements, will be your best chance of making your horse more comfortable. Discuss options with your veterinarian.
Study Reaffirms Benefits of Joint Supplements. www.TheHorse.com/ViewArticle.aspx?id=5794.
Seal Signifies Quality of Animal Supplements. The Horse, December 2004, 18. www.TheHorse.com/ViewArticle.aspx?id=5287.
Ramey, David. Joint Supplements and Vitamins. The Horse, December 2004, 88. www.TheHorse.com/ViewArticle.aspx?id=5264.
About the Author
Stephanie J. Corum received a MS in animal science from the University of Kentucky in Lexington. She has worked in various aspects of the horse industry, including Thoroughbred and Arabian racing, for nearly 20 years. More information about her work can be found at www.theridingwriter.com. She has also published the illustrated children's story Goats With Coats. Currently she and her husband own Charisma Ridge, a small horse farm in Maryland, and she competes in dressage.
POLL: Horse Height