A feed supplement is anything fed to a horse in addition to a natural diet of forage. Technically grain is a supplement. But the term has come to mean any additional nutrients (such as certain vitamins and minerals, extra protein, energy, etc.) that might be lacking in the diet and are added to a horse’s ration. In recent years, a growing number of horse owners have also been feeding herbal supplements and various compounds thought to enhance certain aspects of health and performance.

Horses involved in strenuous activities might benefit from some types of supplements, since high-stress performance depletes some of the body’s nutrients and mineral stores more rapidly than a natural diet of forages can replace them. A wise use of certain supplements could also benefit horses with various health problems. Also, many dietary deficiencies in horses are subclinical (not obvious), so horse owners tend to err on the side of trying to supply additional nutrients in case the horse might have a deficiency.

Some horses are hard keepers, slow healers, have poor stamina, poor reproductive performance, poor hoof growth, or weak hoof horn. These problems and other conditions have stimulated interest in supplements and creation of countless new products. There are many vitamin/mineral supplements–some containing several nutrients, while others contain only a few specific vitamins, such as biotin or thiamine. These supplements are often available in liquid, block, pellet, or powder form–and they’re easy to add to any feeding program.

Editor’s Note: The following is a discussion of some available supplement options. It is not intended as an endorsement of any brand or company.


There are laws that regulate foods and drugs sold in the United States to make sure they are safe for humans and animals. The FDA (Food and Drug Administration) enforces these laws. Nutraceuticals, however, are unregulated, since they fall into neither class. Thus the horse owner cannot assume a product is safe or effective just because it is being manufactured and marketed.

As stated by Amy Gill, PhD, an equine nutritionist in Lexington, Ky., who designed Equi-Force Equine Products, alternative medicine and dietary supplements have grown in popularity as a means of treating various health conditions and illnesses. But, she cautions horse owners about indiscriminant use of these products.

“Some have been researched and others have little or no scientific evidence to support their efficacy,” says Gill. “There are many anecdotal reports on the successful use of many products, however, in treating musculoskeletal conditions, pain, behavioral issues, and as a means to enhance well-being and health.”

Kathleen Crandell, PhD, superintendent of Virginia Tech’s Middleburg Agricultural Research and Extension (MARE) Center, says that many supplements aren’t backed by scientific research, and she doesn’t think they will be. “There is no incentive for companies to have the products tested for efficacy, since they sell even without the expense of the testing, and the price would go up considerably if the manufacturer had to add those costs for research into the product.”

Understanding Supplements

It is important to understand what a product is designed for or intended to do and how it works, before deciding to use it for a specific situation, advises Gill. “It’s also important to remember that supplements can only complement a feeding program, good general management, or veterinary advice,” she says. “They do not provide an absolute alternative.

“Dietary supplements can be divided into several categories, including digestive support, vitamins and minerals, joint and bone maintenance, performance enhancement, hoof and coat health, immune enhancement, treatment of behavioral issues, metabolic disorders, enhancement of weight gain, and so on,” says Gill. Most of these supplements are nutritional and some are nutraceuticals.

Improving Digestion

Some supplements are aimed at feeding the microbes of the hindgut in order to improve digestion of roughages and keep a healthier balance of microbes. Live yeast cultures, for instance, are designed to aid digestion of roughage. Horses prone to colic are often supplemented with yeast, probiotics (friendly bacteria such as Lactobacillus that help break down fibrous parts of forages), and herbs. Proponents believe these supplements have a positive effect on digestion and improve feed utilization.

“Probiotics often include Aspergillus oryzae and yeast,” says Gill. “Yeast culture added to a feed ration can help prevent rapid changes in the intestinal environment, especially when high-starch diets are fed, so this helps stabilize the hindgut. Direct-fed microbials (sources of live, naturally occurring microbes such as Lactobacillus, Streptococcus, and Bifidobacterium) are often fed to horses.”

Mycotoxin binders and MOS (mannan oligosaccharides that bind to Gram- negative bacteria such as Salmonella) are also used in an attempt to bind toxins or substances that might harm the digestive tract and pass them through.

Vitamins and Minerals

“Supplementation with these nutrients is intended to provide additional fortification of diet, as during high-stress levels,” says Gill. Supplementation might also be needed when poor-quality forages are fed, or when feeding growing horses, broodmares in gestation or lactation, or to correct nutritional deficiencies. She believes certain vitamins and minerals help in healing bone/soft tissue injuries, treating metabolic disorders, or when horses undergo intense exercise. But care must be taken to not duplicate and overfeed vitamins and minerals when using supplements.

“Supplemental B vitamins and vitamin C are rarely needed,” she says. “Healthy horses produce vitamin C from glucose in the liver. The B vitamins are produced by microbes in the hindgut.”

Stressed horses, however, might benefit from supplemental vitamin B if their own production can’t keep up with demand, and vitamin C is sometimes helpful if horses are ill, she explains.

Regarding minerals, many of the macrominerals (calcium, phosphorus, sodium, chloride, potassium, magnesium, and sulfur) are often used in electrolyte supplements, or they are fed for their structural role in metabolism (such as bone formation). The microminerals (iron, zinc, copper, manganese, selenium, cobalt, silicon, chromium, etc.) are only needed in very tiny amounts. “Several of these, mostly copper, zinc, and manganese, are best absorbed and utilized when fed as chelates (a chelated mineral is chemically bonded to an amino acid to improve uptake by the digestive system) or proteinates (another organic mineral source),” says Gill.

The microminerals are mainly important in aiding biochemical reactions in the body. As with vitamins, minerals should never be overfed. None of them are safe to feed free-choice except for salt.

Many areas of the country are short on certain minerals, such as iodine, selenium, or copper. Tia Nelson, DVM, a veterinarian and farrier in Helena, Mont., says she saw several foals born this year with contracted tendons due to iodine deficiency. “The trace minerals are very important in fetal development, and you need to know if your region is deficient,” she says. Trace mineral supplements can be mixed with salt or feed.

Joint/Bone Supplements

Glycosaminoglycan (GAG) is one example of a joint supplement that has been reported to help the body repair normal cartilage wear-and-tear in joints. Some advocates say it also seems to prevent inflammation in connective tissue. “Glucosamine, chondroitin, MSM (methylsulfonylmethane), hyaluronic acid, silicon, and other supplements are used to enhance joint health,” says Gill.

Glucosamine is a complex sugar molecule that is a crucial constituent of joint fluid, and chondroitin sulfate is a primary part of joint cartilage. Researchers have said chondroitin sulfate acts as an anti-inflammatory agent capable of inhibiting enzymes responsible for breakdown of cartilage. Studies have shown both nutrients increase the synthetic activity of cartilage-producing cells called chondrocytes, an action that is thought to promote joint repair. Owners have reported horses with degenerative joints receiving glucosamine and chondroitin sulfate supplements have experienced improvement in lameness, flexion, and stride length.

“Silicon is given to horses to enhance bone density/soft tissue elasticity and strength,” says Gill. “Biologically absorbable silicon is thought to increase the uptake of calcium and phosphorus in bone mineralization, and to increase collagen content in the matrix to create more flexible bone.” A large study of racing Quarter Horses fed supplemental silicon experienced significantly fewer injuries than horses not on the supplement.

Nelson suggests the supplement cetyl myristoleate–an omega-5 fatty acid with reported anti-inflammatory properties–as a glucosamine or other joint supplement alternative.

Hoof, Skin, and Hair

There are many products designed to improve hoof health, and some of these are marketed by farrier supply companies. Some are feed additives, others are in treat form. Most contain nutrients and ingredients (such as biotin) thought to promote healthy hoof growth. Biotin is involved in cell growth and division, and it serves an important capacity in the health of all connective tissues, including the skin, cartilage, hair coat, and hooves. Some studies have suggested biotin might have positive effects on hoof growth, but the results suggest that you must keep horses on it for a very long time in order for it to be helpful.

Crandell says it’s important to note that biotin only affects the new growth of the hoof, and that is why you might not see a difference for a long time. It’s also why when you stop feeding it, you can’t see the effects until the new growth becomes visible.

With some supplements you might inadvertently overdo certain minerals, such as selenium, if you are not sure about the mineral content of the rest of the diet, says Nelson. She recommends that you pay special attention to feed labels and consult a veterinarian or nutritionist to ensure you aren’t oversupplementing.

Health Aids

There are many things fed to horses to enhance health. Some of these might be helpful, but others can be harmful, and even some of the beneficial ones are not without risk. Nelson believes flaxseed meal puts a good bloom on a horse’s coat and is also very good for itchy horses or horses with hives. “But it can also increase risk for bleeding,” she explains. “Vitamin E will also increase bleeding time, as will fish oil.”

Performance Enhancement

Wheat germ oil and various vegetable oils and alfalfa contain octacosanol (a long-chain saturated primary alcohol), which proponents say improves stamina and strength. Dimethyl glycine (DMG) is a compound that seems to help equine athletes increase work output and recover faster, and it also seems to improve appetite. The familiar MSM is an organic compound derived from DMSO (dimethyl sulfoxide, which is used topically as an anti- inflammatory). The compound occurs naturally in very small amounts in the bloodstream. Some horse owners use MSM as a supplement to prevent muscle soreness, relieve arthritis, aid in hoof growth, and for a variety of other conditions.

“It’s important to note again that all data from the above-mentioned nutraceuticals are anecdotal, and there have not been any significant benefits found in research studies,” adds Crandell.

Take-Home Message

Remember that “supplements” are just that–substances designed to be additions to a good nutrition and health management program. Supplements are not benign; they can cause illness, or death if given in inappropriate doses or situations. Always discuss your horse’s overall health with your veterinarian, and, if needed, talk to a nutritionist about supplementing your horse’s diet for specific needs or conditions.