Antioxidants are important nutrients for horses that help to combat oxidative stress, maintain overall health, and support performance. They work by neutralizing harmful molecules known as free radicals within the body.

Free radicals are highly reactive molecules with an electrical charge that are produced in the horse’s body during normal metabolic processes. These molecules can accumulate and cause damage to cellular structures in their search to become stable, leading to a range of health issues. This damage is often referred to as oxidative stress (oxidation).

In horses, stressful conditions such as intense exercise, traveling long distances, illness, pregnancy, and advanced age are associated with increased oxidative stress and reduced antioxidant status. Over time, oxidation can contribute to muscle fatigue, impaired performance, inflammation, and chronic disease. [1]

Horses obtain antioxidants naturally through their diet and synthesize some of them in their body. [2] However, in some cases feeding supplemental antioxidants can be beneficial to combat free radicals and safeguard your horse against oxidative stress.

Common antioxidants in the equine diet include vitamins C and E, selenium, zinc, and copper. Other antioxidant supplements that are frequently fed to horses include alpha-lipoic acid, coenzyme Q-10, docosahexaenoic acid (DHA) and acetyl-l-carnitine (ALCAR).

What is an Antioxidant?

Antioxidants are molecules that counteract the damaging effects of highly reactive compounds known as free radicals by neutralizing their electrical charge. Like all living organisms, horses constantly produce free radicals as natural byproducts of metabolic processes. Exposure to heavy metals and environmental toxins also results in oxidative stress. [19]

If left unchecked, these free radical molecules can cause cellular damage to tissues and organs by stealing electrons from other molecules, a process known as oxidation.

Oxidation can affect various molecules within cells, such as DNA, proteins, and lipids in cell membranes. The mitochondria, where cellular energy (ATP) is generated in the presence of oxygen, are particularly vulnerable because of a high concentration of free electrons.

When molecules in cellular structures are oxidized, their functions can be compromised, which can ultimately impact the health of the organism, leading to inflammation, aging, and various diseases.

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Causes of Oxidative Stress

In horses, as in all mammals, oxidation naturally occurs as a result of metabolic processes. Free radicals are naturally produced when nutrients are broken down from the diet to generate energy. [1]

Free radicals do play some important roles in the body, including aiding the immune system in defending against foreign invaders and supporting the adaptive response to exercise. However, an overabundance of these molecules can be detrimental.

However, excessive levels of circulating free radicals are harmful as they can cause damage to muscle, nerve, and skin tissues and promote cell death by destroying cell proteins, DNA, and fatty acids.

Oxidative stress occurs when there’s an imbalance between the production of free radicals and the body’s ability to neutralize them. Oxidative damage is more likely during periods of growth, stress or exertion when the body rapidly breaks down nutrients including protein, carbohydrates, and fat to produce energy. [1]

Oxidative stress is also elevated under the following conditions:

  • Heavy Work: Intense or prolonged exercise can increase the production of free radicals. This is particularly evident in athletes like racehorses after strenuous workouts or competition.
  • Pregnancy and Lactation: Pregnant and lactating broodmares have increased energy demands, resulting in a faster metabolism and increased free radical generation.
  • Environmental Factors: Exposure to environmental pollutants and toxins can contribute to increased free radical generation.
  • Infections and Inflammation: Diseases, infections, or chronic inflammation can lead to increased oxidation. The body’s immune response produces free radicals to combat pathogens, but in excess, these can be detrimental.
  • Psychological Stress: Chronic stress and anxiety can elevate oxidative stress, possibly due to the release of stress hormones. Common stressors for horses include travel, changing social groups and improper management

During periods of increased oxidative stress, antioxidant supplements can help support your horse’s overall well-being and prevent the harmful effects of free radicals.

How Do Antioxidants Work?

Antioxidants are essential for defending against oxidation by quenching free radicals, preventing them from causing cellular damage. They achieve this by donating an electron to the free radical, stabilizing it without becoming unstable themselves.

Free radicals are unstable because they have unpaired electrons, which makes these particles highly reactive. To stabilize themselves, free radicals try to “steal” electrons from neighboring molecules.

When they succeed, they create a new unstable molecule, which then seeks an electron of its own, resulting in a chain reaction that can cause widespread cellular damage if not kept in check.

Antioxidants counteract this process by donating one of their own electrons to the free radical, stabilizing it without becoming unstable themselves. In doing so, they halt the chain reaction and prevent the cascade of cellular damage.

By neutralizing free radicals, antioxidants help maintain the health and integrity of cells, tissues, and organs in the body. [1] Antioxidants are also important for supporting the immune system and maintaining optimal energy production within the body.

Key Benefits of Antioxidants for Horses

Antioxidants offer numerous health benefits to horses, ranging from cellular protection to enhanced immune response.

Cellular Protection:

Antioxidants act as the first line of defense against free radicals, neutralizing these destructive molecules and preventing harm to cells and cellular structures.

Muscle Health and Recovery:

Strenuous exercise and training put a lot of demands on a horse’s muscle cells. This exertion leads to increased production of free radicals, which can contribute to muscle fatigue, soreness, and slower recovery times.

Antioxidants, particularly vitamin E and selenium, play a pivotal role in minimizing exercise-induced oxidative damage, supporting normal muscle repair, and speeding up post-workout recovery. [2][3]

Immune System Support:

A strong immune system is essential for your horse to effectively resist infections and diseases. Oxidative stress can weaken the immune response, making horses more susceptible to illness.

Antioxidants, including vitamin C, bolster the immune system by combating oxidative stress and protecting immune cells from damage. This is particularly important during high-stress events, such as transport, competition, or environmental changes.

Neurological Health:

Horses affected by neurological issues benefit from antioxidant supplementation. [4] Oxidative stress is linked to various neurological disorders in both horses and humans.

Antioxidants support the management of these conditions, by helping to maintain nerve function and contributing to overall neurological health.

Performance Optimization:

Peak performance in equine athletes demands optimal health. Antioxidants contribute to improved performance in competition horses by reducing stress-induced fatigue and supporting efficient energy metabolism.

A diet rich in antioxidants allows horses to maintain their energy and stamina, so they can perform their best during competitions and rigorous training. [5][6]

Aging and Longevity:

As horses age, their natural antioxidant defenses can weaken, rendering them more susceptible to the effects of oxidative stress.

Antioxidant supplementation can support healthy aging by preventing excess oxidative damage that can contribute to age-related diseases.

Sources of Antioxidants

A balanced diet that provides essential amino acids, vitamins, and minerals is key to ensuring your horse has adequate antioxidant defenses. Horses naturally derive some antioxidants from their diet and can also synthesize antioxidant enzyme systems like SOD (superoxide dismutase) and the critically important non-enzymatic antioxidant glutathione in their body.

Many of these systems can regenerate each other. For example, vitamin E converts glutathione into an active form after it has been used and vitamin C regenerates vitamin E.

However, supplemental sources of antioxidants may be beneficial for horses that are ill, older, have high levels of stress, or those in intense exercise and training programs.

Fresh forages, such as pasture grasses, are rich in antioxidants including vitamin E. But stored hay loses Vitamin E over time, so horses might need supplements to prevent a nutritional deficiency.

Many commercial horse supplements and feeds also incorporate antioxidants, although some sources are better than others. Choose organic trace minerals and natural forms of Vitamin E whenever possible to support your horse’s antioxidant status

Top 9 Antioxidant Supplements for Horses

Here are eight of the most popular antioxidant supplements for horses.

1) Vitamin E

Vitamin E is one of the most important antioxidants for horses, helping to protect cell membranes from harm caused by free radicals. [4] A lack of vitamin E in the diet can contribute to nervous system disorders and result in episodes of tying up after exercise. [4]

Exercise and stress increase the production of free radicals, which can deplete vitamin E reserves. Supplementing with vitamin E before events like travel or competition enhances immune function and protects muscle and nerve cells.

Fresh forages and pasture grasses are rich in vitamin E, but its levels can degrade rapidly in stored hay depending on storage and processing techniques. If your horse primarily consumes hay, supplementing with vitamin E is recommended to prevent deficiency.

Equine supplements contain either natural or synthetic forms of vitamin E. Research shows that natural forms containing D-alpha-tocopherol are more effective for increasing vitamin E levels in the horse’s body. [6]

Typical doses of vitamin E supplement for horses range from 2,000 to 5,000 IU per day. [7] However, these studies were done using primarily synthetic, d,l-alpha-tocopherol and you can halve that dose using natural E. Supplements are available in both liquid and powder forms.

Mad Barn’s Natural Vitamin E provides this important antioxidant nutrient in a form that is most efficiently absorbed and utilized in tissues.

Vitamin E

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  • Optimal antioxidant protection
  • Supports exercise recovery
  • Supports immune function
  • Natural with high bioavailability

2) Vitamin C

Vitamin C, also known as ascorbic acid, is a water-soluble antioxidant that protects cells from the damage caused by free radicals. [4] Vitamin C works synergistically with vitamin E, restoring its antioxidant capacity and promoting overall health for your horse.

Vitamin C also assists in the synthesis of collagen, a primary component of connective tissues, making it crucial for wound healing and musculoskeletal health. It is especially important for tendons, ligaments and cartilage in joints.

Horses in good health can synthesize vitamin C in their liver. [4] However, when horses are sick, stressed, or in heavy work, their production of vitamin C may not be sufficient to keep up with their body’s demands.

Supplementing with vitamin C can mitigate the adverse impacts of stress on the immune system. During stressful periods, a common dosage of ascorbic acid for horses ranges from 7 to 10 grams daily.

3) Selenium

Selenium is an essential trace mineral that is a key component of antioxidant enzymes in the horse’s body. This trace mineral works in tandem with vitamin E to scavenge free radicals. [3][8]

Glutathione peroxidases (GPx) is one of the most important antioxidant enzymes that incorporates selenium. This enzyme neutralizes harmful peroxides in the body, preventing them from damaging cells and DNA.

Besides its antioxidant properties, selenium also supports the immune system, aids in thyroid hormone metabolism, and promotes the overall health of muscles and the cardiovascular system in horses. Selenium is also required for:

  • Proper functioning of liver detoxification pathways [3]
  • Muscle development and growth
  • Preventing nerve cell damage caused by free radicals
  • Synthesis of selenocysteine – an essential amino acid

Selenocysteine is derived from methionine where selenium replaces the sulfur. This amino acid is inserted into several proteins including those in antioxidant enzyme systems as well as enzymes which transform T4 thyroid hormone into the active T3 form.

The National Research Council (NRC) recommends that horses consume 2 to 3 mg of selenium per day to ensure optimal immune function. [7]

Horses can obtain selenium in their diet by consuming forage. However, grass or hay grown in selenium-deficient soils may not provide adequate levels, making supplementation necessary.

Mad Barn’s Natural E/Organic Se is a pelleted supplement that provides Natural Vitamin E and organic selenium yeast to support optimal antioxidant status in your horse.

Natural E/Organic Se

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  • Organic selenium yeast
  • Natural Vitamin E
  • Optimal antioxidant status
  • Supports muscle function

4) Zinc

Zinc is another essential trace mineral that is required in the equine diet to support antioxidant defenses. [9] Ensuring your horse gets enough zinc in their diet helps to protect against premature aging and supports healthy tissues and cells.

Zinc is involved in the production of antioxidant enzymes, such as superoxide dismutase (SOD), that convert free radicals into harmless compounds. This enzyme targets and neutralizes the superoxide radical, one of the most common and damaging free radicals found in cells.

Horses undergoing intense exercise generate more free radicals compared to horses at rest and benefit from additional antioxidant support. In one research study, heavily exercised Thoroughbreds were fed an antioxidant supplement containing zinc and copper. The supplemented horses were found to have improved antioxidant capacity while in training. [5]

Senior horses and horses affected by stress or illness may also have lower levels of antioxidant enzymes and could benefit from zinc supplementation. However, it is not recommended to supplement with individual trace minerals, unless you are working with a qualified equine nutritionist who has balanced your horse’s diet.

Instead, choose a balanced vitamin and mineral supplement that provides zinc in the correct ratio to other minerals, such as copper. Furthermore, opt for organic trace minerals, which are bound to amino acids for improved absorption and utilization in the body.

Mad Barn’s AminoTrace+ is a pelleted vitamin and mineral supplement that provides organic trace minerals, including zinc, as well as enhanced levels of other key antioxidant nutrients.


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  • Complete mineral balance
  • Supports metabolic health
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  • Hoof growth

5) Copper

Copper is another essential mineral that serves as an antioxidant by being a component of the enzyme superoxide dismutase. This enzyme is present in almost all cells of the body and protects against free radical damage.

Copper, along with other antioxidants, aids in protecting the horse’s cells, tissues, and organs, ensuring their optimal function. [10] Horses in heavy work and senior horses may need additional copper in their diet to support antioxidant defenses.

Similar to zinc, it is not recommended to supplement with copper as a single ingredient, unless you are working with a qualified nutritionist to balance your horse’s overall diet.

Feeding a balanced vitamin and mineral supplements, such as Mad Barn’s AminoTrace+, will ensure that your horse gets enough copper in their diet to meet their requirement.

6) DHA

DHA, or docosahexaenoic acid, is an omega-3 fatty acid that is known for its anti-inflammatory properties. Research shows that this essential fatty acid also possesses antioxidant effects.

DHA may reduce oxidative stress in horses by inhibiting the production of free radicals and protecting cellular mitochondria (the powerhouse of cells) from oxidative damage. [11] In one study, six horses given a fish oil supplement with DHA had reduced levels of F2-ISO, a biomarker for oxidative stress. [12]

In another study, supplementing horses in training with an oil containing vitamin E and omega-3 fatty acids increased levels of the main antioxidant enzymes, glutathione peroxidase and superoxide dismutase. These findings indicate that vitamin E and omega-3 fatty acids may support post-exercise recovery and performance. [13]

Mad Barn’s w-3 Oil is a fat supplement enriched with microalgae DHA and natural vitamin E to support antioxidant status in horses.

w-3 Oil

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  • Promotes joint comfort
  • Helps to fight inflammation
  • Skin & coat condition
  • Palatable source of Omega-3's

7) Coenzyme Q10

Coenzyme Q10 (CoQ10) is a powerful antioxidant that is synthesized in every cell of the horse’s body. It plays a pivotal role in the production of adenosine triphosphate (ATP), the primary energy source for cells.

Besides directly protecting cells from free radical damage, CoQ10 also supports the antioxidant capacity of other antioxidants, such as vitamins C and E.

Research in horses shows that supplementing with CoQ10 increases antioxidant levels in blood and muscle tissues and helps mitigate oxidative stress. [14]

In a study involving thoroughbred racehorses, researchers observed a significant decrease in plasma CoQ10 level following high-intensity exercise. [15] Lower CoQ10 levels could negatively impact exercise performance, suggesting a possible benefit from supplementation. [15]

Further studies are needed to explore the benefits of giving horses supplemental CoQ10 as an antioxidant.

8) Alpha-Lipoic Acid

Lipoic acid is a naturally occurring fatty acid compound that functions as an antioxidant in the equine body. It protects tissues from free radical damage and can regenerate other antioxidants, such as vitamin C and vitamin E.

Because it is both water- and fat-soluble, lipoic acid can work throughout the entire body, protecting a wide range of tissues. Lipoic acid also plays a key role in energy metabolism within cells, especially in mitochondria.

Alpha-lipoic acid (ALA) is a synthetic form of this compound that is commonly used in equine supplements.

Research in horses shows that ALA is beneficial for reducing markers of oxidative stress during exercise in blood serum and muscle tissues. [16][17][18] In these studies, typical dosages of ALA range from 10-25 mg/kg body weight per day.

9) Acetyl-l-carnitine (ALCAR)

ALCAR is a naturally occurring metabolite of L-carnitine that is generated in large amounts during exercise. It serves to signal increased levels of antioxidants and reduce levels of inflammatory cytokines. [20] It is particularly abundant in the brain, nervous system and skeletal muscle.

Acetyl-l-carnitine enhances nerve regeneration after nervous system injury. [21] It is also useful for neuropathic pain, such as that which accompanies chronic laminitis. [22]

ALCAR supports mitochondrial biogenesis, helping to form new mitochondria in cells. [23] It also activates AMPK, a key energy-sensing enzyme which directs glucose away from glycogen formation and into energy-producing pathways. [24] These two properties make it useful for muscular function in general and to support horses with PSSM.


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  • Supports energy metabolism
  • Supports muscle function
  • Reproductive function
  • Competition horses


Antioxidants are molecules that help neutralize free radicals, protecting the horse’s body from oxidative stress. [1] Antioxidants protect your horse by:

  • Scavenging free radicals to render them inactive
  • Inhibiting the cascade of oxidative damage
  • Promoting repair of damaged tissues and cells

The best way to protect your horse’s health is to feed a balanced diet that is rich in antioxidants, including essential vitamins and minerals such as selenium, copper, zinc, vitamin C, vitamin E and the sulfur-containing amino acid methionine.

Oxidative stress is associated with high-intensity exercise, illness, nutritional deficiency, psychological stress and periods of rapid growth or high energy demands.

Horses experiencing higher levels of oxidative stress may need additional support from antioxidant supplements.

Wondering if your horse could benefit from antioxidant supplementation? Submit your horse’s information online for a free consultation with our qualified equine nutritionists.

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  1. Halliwell B. and Gutteridge J.M.C., Free Radicals in Biology and Medicine. 2015.
  2. Garcia E.I.C. et al., Dietary Supplements of Vitamins E, C, and β-Carotene to Reduce Oxidative Stress in Horses: An Overview. J Equine Vet Sci. 2022.View Summary
  3. Culhuac E.B. et al., Influence of Dietary Selenium on the Oxidative Stress in Horses. Biol Trace Elem Res. 2023. View Summary
  4. Finno C.J. and Valberg S.J., A Comparative Review of Vitamin E and Associated Equine Disorders. J Vet Intern Med. 2012. View Summary
  5. Williams C.A., The Effect of Oxidative Stress during Exercise in the Horse. J Anim Sci. 2016. View Summary
  6. Fagan M.M. et al., Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses. J Equine Vet Sci. 2020. View Summary
  7. Nutrient Requirements of Horses: Sixth Revised Edition. National Academies Press. 2007.
  8. Ony E.E., Selenium for Horses: How Important Is It?. 1999. Accessed Aug. 14, 2023.
  9. Marreiro D. do N. et al., Zinc and Oxidative Stress: Current Mechanisms. Antioxidants (Basel). 2017.
  10. Gaetke L.M. and Chow C.K., Copper Toxicity, Oxidative Stress, and Antioxidant Nutrients. Toxicology. 2003.
  11. Li G. et al., Antioxidant Activity of Docosahexaenoic Acid (DHA) and Its Regulatory Roles in Mitochondria. J Agric Food Chem. 2021.
  12. White-Springer S.H. et al., Dietary Omega-3 Fatty Acid Supplementation Does Not Impair Vitamin E Status or Promote Lipid Peroxidation in Growing Horses. J Anim Sci. 2021. View Summary
  13. S M. et al., Oil Supplementation Produces an Increase in Antioxidant Biomarkers in Four-Beat Gaited Horses. Presented at the Equine Veterinary Journal June 17, 2014.
  14. Sinatra S.T. et al., Coenzyme Q10 in Equine Serum: Response to Supplementation. J Equine Vet Sci. 2013.
  15. Sinatra S.T. et al., Plasma Coenzyme Q10 and Tocopherols in Thoroughbred Race Horses: Effect of Coenzyme Q10 Supplementation and Exercise. J Equine Vet Sci. 2014.
  16. Rezaei Zonooz S. et al., Effect of Alpha-Lipoic Acid on Oxidative Stress Parameters: A Systematic Review and Meta-Analysis. J Funct Foods. 2021.
  17. Williams C.A. et al., Lipoic Acid as an Antioxidant in Mature Thoroughbred Geldings: A Preliminary Study. J Nutr. 2002. View Summary
  18. Kinnunen S. et al., Alpha-Lipoic Acid Modulates Thiol Antioxidant Defenses and Attenuates Exercise-Induced Oxidative Stress in Standardbred Trotters. Free Radic Res. 2009.
  19. Ercal, N. et al. Toxic Metals and Oxidative Stress Part I: Mechanisms Involved in Metal-induced Oxidative Damage. Curr Top Med Chem. 2001.
  20. Wang, S. et al. Anti-Inflammatory and Antioxidant Effects of Acetyl-L-Carnitine on Atherosclerotic Rats. Med Sci Monit. 2020.
  21. Pourshahidi, S. et al. The Effect of Acetyl-L-Carnitine (ALCAR) on Peripheral Nerve Regeneration in Animal Models: A Systematic Review. Neurochem Res. 2023.
  22. Sarzi-Puttini, P. et al. Acetyl-L-carnitine in chronic pain: A narrative review. Pharmacol Res. 2021.
  23. Nicassio, L. et al. Dietary supplementation with acetyl-l-carnitine counteracts age-related alterations of mitochondrial biogenesis, dynamics and antioxidant defenses in brain of old rats. Exp Gerontol. 2017.
  24. Zhang, Z. et al. Acetyl-l-carnitine inhibits TNF-alpha-induced insulin resistance via AMPK pathway in rat skeletal muscle cells. FEBS Lett. 2009.