Among the most widely advertised supplements for horses are products that contain glucosamine salts, chondroitin sulfate, or both. From an economic standpoint, these products are wildly successful; the market for such products in the human fields is around one BILLION dollars. However – and perhaps amazingly – there is very little evidence to show that they actually work. I personally believe that the products are a waste of money (and they are expensive), being sold mostly on promise, with little in the way of positive results obtained from good trials. Here’s some information about the products in horses that might help you make up your own mind.
Glucosamine is an sugar compound that is made in the horses body. It’s incorporated into many of the horse’s body’s molecules, including joint cartilage, however, it is NOT necessary for the synthesis of cartilage (the body uses the sugar, glucose, to build cartilage). Small amounts of glucosamine can detected in the bloodstream of horses, but no deficiency has ever been reported, in any species. The glucosamine that you may buy for your horse comes mostly from the shells of crustaceans.
A number of test-tube studies have shown that glucosamine has biological activity, and various beneficial effects on cartilage cells. While this should be great news, it should be noted that these studies have generally been conducted with levels of glucosamine that can’t be reached when the substance is fed to horses. In fact, only 2 – 5% of the glucosamine that is fed to the horse actually is available for the horse, and, at the levels normally fed, it’s hard to see how it could have any effect at all on the horse (the test tube studies are usually conducted at concentrations from 200 – 2000 times higher than what can be reached by feeding the stuff). Even though one test tube study, done on cultured horse cartilage cells, did show beneficial effects, those effects still haven’t been shown to occur in living horses. Thus, in general, there’s good reason to doubt whether ANY of the information obtained from test tube studies is relevant to preventing or treating arthritis in horses.
It has recently been shown that glucosamine levels are higher when horse joints are inflamed. This raises the possibility that glucosamine might be useful in joints to treat arthritis. There’s also some suggestion – obtained from work in mice – that glucosamine could have some indirect effects by reducing products of inflammation produced in the liver. But the fact is that no matter how interesting these experimental results, they have yet to be shown to be important clinically in actual horses.
Perhaps amazingly, given the amount of product sold, there have been no clinical studies on the effectiveness of orally administered glucosamine by itself for the treatment or prevention of arthritis in horses. Even so, the information obtained from other species suggest that while results are often positive, the effects are very mild, and probably not really very important. In humans, even though there have been many clinical trials on glucosamine, there’s still much controversy as whether it’s effective. Most well-conducted, large, independently-funded clinical trials in humans show no effect at all (on the other hand, when industry pays for the trials, they are five times more likely to be effective)!
There are two glucosamine salts – glucosamine hydrochloride, and sulphate. Some people have suggested that the horse’s intestinal tract absorbs the two compounds differently, and thus assert that glucosamine sulphate may be more effective. However, in the horse’s stomach, both compounds ar split into glucosamine, so it’s hard to see why that would be true. Even though one study, in horses, shows that the glucosamine sulphate preparation reaches higher levels in the joints (compared to the hydrochloride salt), the levels aren’t so different as to be clinically relevant, and might just mean that the sulphate preparation tasted better (and the horses ate more of it).
Horse owners should be be aware that the products being sold to them may not contain much glucosamine in them. Two studies (including one by Dr. Ramey), show that there is a huge variation in the amount of glucosamine available in the products. Otherwise stated: there may not be much glucosamine in your horse’s glucosamine.
The currently recommended doses of glucosamine are about 20 mg/kg. For most average horses, that means a dose of around 2000 mg a day.
Chondroitin sulfate (CS) is a sugar molecule found in cartilage, bone, tendons, and ligaments. The CS fed to horses comes from animal sources (cow, chicken, pork, and even marine cartilage), so the actual make-up of the product fed to horses depends on where it comes from. Because of this, there is also variation in absorption, which is another reason for concern.
It’s an open question whether any CS is absorbed at all. In humans, ingesting CS, doesn’t change blood levels; if blood levels don’t increase, it can’t have any direct effects on joints! Some people have suggested indirect effects, due to elevated levels in the intestine, or in the liver, but this is just speculation, and hasn’t been demonstrated. The fact that CS isn’t well absorbed also casts doubt on the relevance of all of the test tube studies; if it can’t get into the body, who cares what happens in the test tube?
So far, there has only been one clinical experimental study in horses that looked at the effects of CS given in the muscle; no beneficial effects were noted. In addition, different CS compounds that come from different manufacturers act differently in test tube experiments. This, of course, means that you unless you know specifically what’s in the product you’re feeding to your horse, you can’t anticipate any positive result.
COMBINATION OF CHONDROITIN SULFATE AND GLUCOSAMINE
While there’s a large amount of conflicting evidence, from many species, three clinical trials have looked at the combination of glucosamine hydrochloride and CS specifically in horses. All of them have reported beneficial effects on symptoms of joint disease; all of them were funded by industry. The most recent study, which did appear to be well-conducted, suggested that the combination offered some symptomatic relief in lameness.
There don’t appear to be any side effects associated with the use of the combination, and 5 times the recommended dose can be safely administered to horses. That’s not necessarily a good thing, however; in people, when glucosamine is combined with CS, the levels of glucosamine measured in the blood are lower than those reached when glucosamine is given alone. This suggests that CS actually inhibits glucosamine absorption.
THE BOTTOM LINE
If you’re looking for a readily available product to give to you horse in hopes of treating arthritis, there are plenty of them for you to buy. However, you may not be buying what you think you’re buying, and there’s little reason to believe that the products will help your horse.