What's the Scoop?

With hundreds of equine nutritional supplements on the market, it's hard to know exactly which one your horse might need, if any at all. While not every horse requires supplements, they can be beneficial in specific circumstances.

According to Paul Siciliano, PhD, associate professor in the Department of Animal Sciences at Colorado State University, "A supplement is useful only when it provides nutrients that are lacking in the horse's base diet."

The Base Diet: Forage and Feed

Proper nutrition begins with quality forage and feed. Frederick Harper, PhD, extension horse specialist at the University of Tennessee, says, "If you aren't feeding good hay, you might need to add a nutritional supplement to your horse's diet."

Harper emphasizes that the importance of forage shouldn't be underestimated. "Some horse owners consider hay and pastures to be nothing more than fillers or pacifiers," he says. "In reality, forages have a great deal of nutritional value, and play a major role in the horse's diet."

According to Laurie Lawrence, PhD, professor of equine nutrition at the University of Kentucky, "Horses should be fed a commercially prepared feed mix that is specifically formulated for their physical condition and physiological class."

Reputable manufacturers are those that maintain a quality control program, says Gary Potter, PhD, professor emeritus at Texas A&M University and owner of Potter Enterprises, an equine consulting firm.

These companies not only analyze the nutritional value of the ingredients going into the feed, but also the end product.

"There may be some processing losses in feed," says Potter. "Proteins, amino acids, and minerals usually go through processing intact, but some unstable vitamins are highly susceptible to heat and pressure and may be affected by processing. The best feed companies try to allow for these losses by performing post-processing analyses."

Need for Supplementation

"Many horse owners buy a commercially prepared feed and mix it half-and-half with oats," Potter says. "This practice can be a problem for weanlings, lactating mares, and performance horses."

When extra ingredients are introduced to the feed mix, the nutritional balance is altered, and it becomes necessary to add supplements to offset the lost nutrients.

Nutritional supplements also might be necessary for horses fed reduced rations for health reasons. "Horses at risk for founder or colic may not be able to tolerate a quantity of grain sufficient to provide good nutrition," says Harper.

Another case in which supplementation might be necessary is when horses of different age groups or physiological classes are being fed together.

"If it's inconvenient to give horses several different types of feed, you may want to add a specific supplement to the ration of one horse, but not another," says Lawrence.

Vitamin Supplements

Brian Nielsen, PhD, equine exercise physiologist in the Department of Animal Sciences at Michigan State University, says, "Extra vitamins aren't necessary for every horse, but for hard-working performance horses, a vitamin supplement may stimulate appetite and help them avoid becoming underweight."

Since quality forages are rich in vitamins, deficiencies are relatively rare. Still, many horse owners feed vitamin supplements, especially vitamin E and biotin.

Vitamin E

For performance horses and those eating rations relatively high in fat, vitamin E supplementation is often beneficial.

Harper notes, "As an antioxidant, vitamin E works to block free radicals from attacking lipids and forming harmful lipid peroxides in the body, which can cause oxidation-induced tissue damage."

In horses that are working hard or otherwise stressed, tissue damage caused by the oxidation process is accelerated.

"When fed as a supplement to performance horses, Vitamin E may help delay fatigue, increase endurance, and accelerate healing," says Harper.


The B vitamin biotin is a popular supplement typically found in hoof health products. Biotin is involved in the process of cell growth and division, and it plays an important role in the health of all connective tissues, including the skin, cartilage, hair coat, and hooves.

"A few studies have shown that biotin may have positive effects on hoof growth," notes Nielsen. "However, these studies suggest that you have to keep horses on it for a long period of time in order for it to be beneficial. Many researchers are skeptical that biotin has much effect, unless it is deficient in the diet."

Minerals and Electrolytes

When horses are fed quality feed and forages, and they have access to salt and mineral blocks, most are able to get all the minerals they need for good health.

For equine athletes, and for horses working in hot weather that sweat excessively, the extra minerals provided by electrolyte supplements often become necessary.

"Manufacturers can't put enough electrolytes in commercial feed preparations to satisfy the needs of heavily stressed horses because it would make the feeds unpalatable," explains Potter.

The minerals typically found in electrolyte supplements--sodium, chloride, and potassium--are included to replace those lost when horses sweat.

Electrolyte preparations are available as powders and liquids that can be added to feed or water, or as pastes and gels that are administered orally to the horse.

"For horses that are being fed grain regularly, it's best to add mineral and electrolyte supplements to the feed, so you can make sure they're getting what they need," Potter says.

It's important to note that if used improperly, electroltyes can lead to metabolic imbalances in the horse.

"It's also important to make sure that the horse has plenty of fresh water available," notes Lawrence. "When you add a lot of these electrolytes to the diet, horses urinate more and drink more."


Selenium is a trace mineral that is often used as a stand-alone nutritional supplement. Selenium is readily available in plants grown in soil that contains adequate amounts of the mineral. In some regions of the United States, soils are deficient in selenium while in other areas, soil levels are high enough to be considered toxic.

"Before adding a selenium supplement to your horse's diet, it's important to determine the selenium content of the feeds and forages your horse is eating," Harper cautions.

The selenium content in grain is listed on the feed label. However, to test the selenium content in your horse's forage, Harper recommends using a company such as Dairy One to test your hay and grass.

While horses require 3 milligrams of selenium per day, daily doses of 5 milligrams or more can cause mild to severe toxicity in horses.

Essential Fatty Acids

Most horse's feed rations are very low in fat--typically less than 3-4% by weight. Research suggests that when introduced gradually, horses can tolerate up to 20% of their daily caloric intake in the form of fat.

Some dietary fat is necessary to facilitate absorption of the fat-soluble vitamins, including vitamins A, D, E, and K, and there's little doubt that adding even small quantities of fat to the equine diet improves the condition and appearance of the skin, hooves, and hair coat.

"The benefits of fat supplements are most applicable to high-stress, working horses," says Potter. "Because fat is high in calories, you can feed less grain and reduce some of the soluble carbohydrates when you add it to the ration."

Research has demonstrated that increasing the fat in a horse's diet to about 10% (or 20% of the total calories) promotes greater stamina and endurance in working horses.

Horses also require small amounts of the essential fatty acids (EFA) omega-3 and omega-6. Some equine studies have shown that changing the ratio of essential fatty acids in the diet dampens the production of certain prostaglandins involved in inflammation processes.

"Increasing the ratio of omega-3 to omega-6 fatty acids in the diet helps suppress the inflammatory response in horses' joints and airways," Potter says.

Supplementing rations with flaxseed, cold-processed soybean oil, and fish oils improves the ratio of omega-3 to omega-6 fatty acids.

Joint Supplements

Glucosamine and chondroitin sulfate are typically found in nutritional supplements designed to treat osteoarthritis and promote equine joint health.

Glucosamine is a complex sugar molecule that is an important constituent of joint fluid, while chondroitin sulfate is a primary component of joint cartilage.

Chondroitin sulfate is thought to act as an anti-inflammatory agent capable of inhibiting enzymes responsible for cartilage breakdown. In laboratory studies, both nutrients have been shown to increase the synthetic activity of cartilage-producing cells called chondrocytes, an action believed to promote joint repair.

Glucosamine and chondroitin sulfate supplements come in a variety of forms, including pills, powders, pastes, liquids, and wafers. The glucosamine supplements are derived from chitin, found in the shells of lobsters and crabs. Chondroitin sulfate typically is extracted from bovine tracheal cartilage. According to Nielsen, "Glucosamine and chondroitin sulfate supplements may offer protective effects against joint injury. When fed to horses with degenerative joint disease, some researchers have reported improvements in lameness, flexion, and stride length."

Another joint supplement is silicon, which is thought to play a role in bone formation and repair. Though a bit mysterious, research has demonstrated the element might enhance performance and play a role in the reduction of injury rates. There are commercially available supplements that offer a source of silicon.

"Silicon supplementation appears to be able to make a dramatic difference in terms of performance," Nielson says.

In a large study of racing Quarter Horses, those fed a supplemental silicon experienced significantly fewer injuries compared to horses not receiving the supplement.

Yet another commonly used joint supplement is methylsulfonylmethane (MSM), which is in the form of a tasteless, odorless, white powder. It is an organic compound derived from dimethylsulfoxide (DMSO), a topical agent used to reduce swelling.

"Many researchers believe that the primary benefit of feeding MSM is to restore proper sulfur concentrations in the diet," says Nielsen. Sulfur is necessary for the formation of connective tissue.


Probiotic supplementation in the equine diet is a relatively new concept. As a result, its utility in the equine diet isn't fully understood. Probiotic supplements, available in liquids, powders, and pastes, contain live bacterial cultures that are believed to restore or enhance the natural bacterial inhabitants in the digestive tract.

"For the average healthy horse, probiotics probably aren't necessary," Nielsen says. "In a few circumstances, it might be useful to give a probiotic supplement; for instance, after a horse has been treated with antibiotics."

While antibiotic medications kill bacterial pathogens responsible for a number of infections, the drugs also kill off some of the beneficial microorganisms in the equine gut, including those that aid in digestion and immunity.

There is evidence to suggest that feeding probiotics might benefit horses with acute enterocolitis (inflammation of the small intestine and colon). In some cases, however, researchers have failed to demonstrate favorable results associated with probiotic supplementation.

"All probiotics are not equal," notes Siciliano. "Some may have favorable properties regarding their effect on the equine hindgut environment, but the real benefit of probiotic supplementation in horses remains to be determined."

The Bottom Line

"It's easy to think that if feeding a little bit of a particular supplement is good, then feeding a lot of it is even better, but that's not the way it works," says Potter. "In most cases, over-supplementation is more of a problem than not supplementing at all."

To avoid under- or over-supplementing your animal, and to ensure that your horse is getting the best-balanced diet, consult with an equine nutritionist or veterinarian about your horse's feeding regimen.

About the Author

Rallie McAllister, MD

Rallie McAllister, MD, grew up on a horse farm in Tennessee, and has raised and trained horses all of her life. She now lives in Lexington, Ky., on a horse farm with her husband and three sons. In addition to her practice of emergency and corporate medicine, she is a syndicated columnist (Your Health by Dr. Rallie McAllister), and the author of four health-realted books, including Riding For Life, published by Eclipse Press and available at www.ExclusivelyEquine.com or by calling 800/582-5604.

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