Oral Supplements in the Treatment and Prevention of Equine Joint Diseases
I M Wright MA VetMB DEO DipECVS MRCVS
Chondroitin Sulphate
Chondroitin sulphate consists of repeating units of the disaccharide galactosamine and glucoronic acid but unlike polysulphonated glycosaminoglycans there is only one sulphate group per disaccharide compared to three to four in each polysulphated glycosaminoglycan.
In vitro studies have demonstrated anti-inflammatory properties of chondroitin sulphate and it has also been shown to inhibit hyaluronidases. In long term clinical trials of injectable chondroitin sulphate the course of osteoarthritis was slowed, joint function improved, joint pain reduced and analgesic usage reduced. However, there is little evidence to support the enteral absorption of chondroitin sulphate in horses. In man some publications suggest that there is absorption while other demonstrate no effective absorption. There is evidence of absorption in dogs but it appears that chondroitin sulphate is not absorbed following oral administration in rabbits. The balance of scientific evidence currently indicates that absorption of chondroitin sulphate is unlikely in herbivores, probably does take place in carnivores, and may or may not be present in omnivores, This equates with basic nutritional physiology and probably applies also to the absorption of crude cartilage supplements and extracts of both mammalian and fish (usually shark) origins. Oral chondroitin sulphate has largely fallen into disuse in the treatment or prevention of human joint disorders.
In some preparations chondroitin sulphate is combined with glucosamine but in the majority of currently available products the recommended doses provide insufficient glucosamine. There are two published clinical studies of such supplements in horses; both involved the product “Cosequin”. The first was a controlled study in which the supplement was given to horses with experimentally (chemically) induced joint disease; supplementation failed to demonstrate any benefit in the parameters measured. In the second, uncontrolled study some non-specific benefits (reduced lameness, improved flexion etc.) were reported.
Glucosamine
Glucosamine is a precursor of the disaccharide units of articular cartilage glycosaminoglycans. There is good evidence of oral bio-availability and tropism for articular cartilage after oral administration in man. It has also been demonstrated that exogenous glucosamine is incorporated into newly synthesised glycosaminoglycan. Glucosamine can be given as the sulphate or hydrochloride as there is gastric disassociation of the salts.
In vitro studies have shown that glucosamine produced increased glycosaminoglycan, proteoglycan and collagen synthesis and stimulated production of hyaluronan. In vivo studies reported anti-inflammatory activity including inhibition of superoxide radical generation and inhibition of lysosomol enzyme activity.
There are 9 studies published in Europe since 1980 that have all demonstrated improved physical performance in people with joint pain. These included double blind trials when glucosamine was compared with a placebo for the treatment of osteoarthritis of the knee. In a second study oral glucosamine was as effective as ibuprofen in relieving the symptoms of osteoarthritis of the knee and in a further study reversal of cartilage degeneration was demonstrated by electron microscopic examination of cartilage biopsies taken before and after treatment with oral glucosamine.
Glucosamine is chondroprotective as defined by Ghosh and Smith (1992) and is classified as “a symptomatic slow-acting drug” by the International League Against Rheumatism. The accepted dosage in man is 1,500mg of glucosamine per day so with extrapolation to the horse the dose is considered to be 10 grams per day.
Current evidence suggests that when there is a role for oral supplementation in the treatment or prevention of equine joint diseases then glucosamine is the supplement of choice.