Oxidation occurs naturally in the horse’s body as it breaks down nutrients. This essential process generates reactive oxygen species—better known as free radicals—that can cause cellular damage. Supporting the horse’s antioxidant defenses helps maintain their long-term health and performance.

Antioxidants for Overall Horse Health

Antioxidants protect cells from damage caused by oxidative stress. “Oxidation occurs when nutrients are broken down and converted to energy, and this process is constantly occurring in the horse’s body,” says Kelly Vineyard, PhD, equine nutritionist and owner of EquiVine PhD Nutrition, based in Gainesville, Florida. “Oxidation rates increase as energy needs increase, such as during exercise, growth, pregnancy, and anytime the body is stressed.”

Because oxidation doesn’t occur perfectly, it produces free radicals—molecules with unpaired electrons that seek to stabilize by binding to other cells. In the process these radicals damage muscle, immune, and nerve tissue.

Meanwhile, antioxidants neutralize the free radicals, and the horse needs a steady supply of them. “Horses can synthesize some antioxidants in their body, but they also need antioxidants from their diet to ensure adequate protection against free radical damage,” Vineyard says.

Antioxidant Requirements in Equine Diets

Several nutrients act as antioxidants, including vitamins E, A, and C, and the mineral selenium. “If there are not enough antioxidants present in the body to combat the potential oxidative damage that occurs as a byproduct of exercise, pregnancy, illness, etc., then the horse can experience muscle cell damage (fatigue and tying-up), immune cell damage (decreased immune function), and nerve cell damage (degenerative diseases such as equine motor neuron disease),” Vineyard says.

The National Research Council’s (NRC) Nutrient Requirements of Horses (2007) outlines established guidelines for vitamin E, selenium, and vitamin A. “There is no official NRC requirement for vitamin C because healthy horses can synthesize it on their own,” says Vineyard. “However, stressed horses might not be able to synthesize adequate amounts of vitamin C, so short-term supplementation in certain cases could be beneficial.”

Meeting NRC guidelines through a well-balanced diet should serve as the first step in providing antioxidant support. Most ration balancers or fortified feeds, when fed at recommended rates, meet these vitamin and mineral requirements.

“In addition to required nutrients, several other antioxidant compounds can benefit horses, including coenzyme Q10, alpha-lipoic acid, and plant-derived polyphenols,” Vineyard adds.

Tailoring a balanced diet to the individual horse helps reduce the risk of oxidative damage.

When to Add Antioxidants to Your Horse’s Diet

Before reaching for a supplement, evaluate the horse’s entire nutrition program. “Focusing on feeding a balanced diet that includes plenty of good-quality forage, paired with an appropriate balancer or concentrated feed to supply additional calories and/or essential nutrients is a good place to start,” Vineyard says.

For healthy horses at maintenance, again, a well-balanced diet often provides adequate antioxidant levels. However, horses with limited pasture access or those that exercise, breed, face stress, or are growing might need additional antioxidant support.

A qualified equine nutritionist can also help you determine whether your horse needs additional supplementation. Avoid oversupplementing, which could lead to dietary excess and waste.

Choosing a High-Quality Antioxidant Supplement

Horse owners have a wide range of options when shopping for supplements. Evaluating products critically can save money and ensure effective support.

“This goes for any type of nutritional supplement, but owners should look for a supplement from a reputable company that takes reasonable measures to ensure safety, quality, and efficacy of the product,” says Vineyard. “This might include research trials conducted in horses, labeling transparency, third-party testing, and/or affiliation with an organization like the National Animal Supplement Council that signals a commitment to quality.”

Oxidative Stress and Equine Joint Health

Joint health remains a key concern for horse owners, especially those with competition and hard-working animals. Exercise places stress on joints, and oxidative damage in these areas can contribute to degenerative joint disease.

“Degenerative joint disease, also known as arthritis, is characterized by the breakdown of cartilage in the joint and causes pain, stiffness, and decreased range of motion,” says Vineyard. “Excess oxidative damage in the joint has been implicated in the progression of degenerative joint disease, and antioxidants can help protect against this damage and potentially slow its progression.”

Owners can adjust both management and nutrition to reduce the risk of joint disease, but they should again start with a balanced diet that meets all their horses’ nutrient requirements. Many hope supplements will provide quick solutions, but meaningful results often take time. Also, keep in mind that overuse won’t necessarily offer added benefits.

“I do not consider antioxidants as a first line of defense against joint disease,” says Vineyard. “But as part of a comprehensive joint health support program, antioxidants certainly play a key role in preventing excessive oxidative damage to cartilage cells, and they could be included as part of a comprehensive supplement that specifically targets joint health.”

Take-Home Message

Antioxidants play an essential role in defending against oxidative damage, which can affect physical performance, immune function, and joint health. Horses need adequate vitamin A, E, and selenium requirements to stay healthy. “Any supplementation above and beyond requirements should be considered as part of the overall ration and strategically utilized to meet a specific need,” Vineyard says. “Dietary supplementation of antioxidants as an insurance policy or ‘just in case’ is a poor strategy that, at best, will be a waste of money and, at worst, result in a detrimental dietary excess.”