CHAPTER 21 Use of Nutraceuticals for Equine Joint Disease
Joint supplements (nutraceuticals) have been the focus of much debate in both the human and veterinary literature, and confusion exists regarding product selection, specific application, and expected efficacy. These agents are thought to prevent or slow the progressive deterioration of articular cartilage by (1) counteracting inflammation, (2) reducing articular cartilage degradation, and (3) stimulating cartilage synthesis.
Joint supplements are loosely classified as nutraceuticals. The term nutraceutical combines the word nutrient (nourishing food or food component) with pharmaceutical (a medical drug). The word nutraceutical has been used to describe a broad list of products sold under the premise of being a dietary supplement (i.e., a food) but for the expressed intent of treating or preventing disease.
The claims made by manufacturers that these supplements aid in maintaining equine joint health are scientifically weak. The potential difference between a feed and a nutraceutical is that the latter is unlikely to have an established nutritive value. Feeds are required to have nutritive value and are accountable, via labeling, for these values. Joint supplements fall somewhere in between food and drugs, but they are not required to list ingredients or nutrient profiles as required by feeds, and in many cases they are intended to treat or prevent disease without first undergoing proper drug approval.
Joint supplements are fed to horses for one of two purposes. The first is to heal a diseased joint or make a chronically unsound horse sound. The second reason for feeding oral joint supplements is to prevent joint problems from developing. Assuming effect when these supplements are used in the first instances is flawed because often treatment is initiated without a veterinary examination and the source of lameness is never diagnosed. The veracity of the second premise is difficult to disprove but is nevertheless the basis for high frequency of empiric administration of some licensed drugs as well as nutraceuticals.
In 2005 nutraceutical sales reached more than one billion dollars for the companion animal market in the United States. That number is expected to double in the next 3 years. More than 100 equine nutraceutical products are currently on the market in the United States. This is a disturbing trend for an industry that, for the most part, is unregulated by the Food and Drug Administration (FDA) and for which claims of product efficacy have little scientific basis.
None of the oral supplements or oral nutraceuticals is licensed by the FDA, and proof of efficacy is generally lacking. Most products contain glucosamine or chondroitin sulfate or both, along with other added ingredients. Historically, the oral glycosaminoglycan products that were initially available for the horse included a chondroitin sulfate product from bovine trachea and a complex of glycosaminoglycans and other nutrients from the sea mussel Perna canaliculus. A combination of glucosamine hydrochloride (glucosamine), chondroitin sulfate, manganese, and vitamin C has been marketed as a nutraceutical,∗ and a number of other products have simulated this product. Since that time, other products have attempted to compete on the basis of decreased cost (with no demonstration of comparable efficacy) or other added ingredients.
Glucosamine sulfate is a precursor of the disaccharide subunits of cartilage proteoglycans. Although glucosamine salts are reportedly well absorbed after oral administration in humans, one study reported oral bioavailability of glucosamine in horses to be only 2.5%, with a large volume of distribution, which the authors interpreted as poor absorption from the intestinal tract but extensive tissue uptake.