by Casie Bazay

How to Reduce Oxidative Stress in Horses

How to Reduce Oxidative Stress in Horses

Like us, horses are no strangers to experiencing stress. Intense exercise, transport, changes in management routines– these can all lead to stress which may affect a horse’s behavior, appetite, and health in the short-term. 

However, horses also share another related phenomenon with us: They, too, experience oxidative stress which directly affects the aging process and is linked with many different chronic health conditions.  

What is Oxidative Stress?

Oxidation is a natural process that occurs when oxygen combines with various other elements in the body during metabolism. 

The rate of oxidation will depend on the activity and life stage of the animal, however. For example, at rest, the rate of oxidation is lowest, but during exercise, stress, pregnancy, or lactation, the rate of oxidation increases.

When oxidation rates increase, it’s often referred to as oxidative stress. An imbalance exists between production and accumulation of oxygen reactive species (ROS), also known as free radicals, and the body’s ability to detoxify these reactive products. 

This increase in ROS causes damage to healthy cells and leads to decreased immune function, illness, or nervous system dysfunction within the animal.  

In people, oxidative stress is linked with diseases such as diabetes and cancer. In horses, it’s linked to Cushing’s disease and may also play a role in many other diseases such as osteoarthritis, recurrent airway obstruction, and laminitis

Causes of Oxidative Stress and Inflammation

While it’s true that moderate exercise can have beneficial effects on overall health and the immune system, strenuous exercise, such as endurance racing, may have a detrimental effect on the immune system and cause oxidative stress. 

Increased exercise levels increase nutrient and antioxidant needs as well, and if these needs aren’t met, oxidation will occur at a higher rate. 

Other causes of oxidative stress include infection, inflammation, UV radiation exposure, and certain environmental conditions (such as air pollution). Even cold weather can lead to oxidative stress in horses.

Antioxidants Help Fight Oxidative Stress in Horses

Antioxidants include vitamins, minerals, enzymes, and proteins that must be synthesized in the horse’s body or consumed in the diet. They help to slow down the rate of oxidation and prevent damage from free radicals. Therefore, they are a critical part of any horse’s diet

Most horses on green pasture are likely getting plenty of antioxidants in their diet. However, many horses do not (or cannot) have access to green pasture. Additionally, the process of drying and curing hay destroys most of the antioxidants present within the plants. 

Aside from horses in hard work, it’s also possible that others might need more antioxidants than what pasture can provide, such as in the following cases:

  • Older horses;
  • Growing horses;
  • Ill, injured, or immune-compromised horses; and
  • Horses with allergies.

There are a number of ways to provide supplemental antioxidants in your horse’s diet, but the basics of sound antioxidant nutrition include adequate intake of vitamin E, vitamin A, and trace minerals. 

Vitamin A (Retinol)

Green grass and most commercial feeds are plentiful in vitamin A, and fresh hay contains some vitamin A as well (vitamin A decreases the longer hay is stored). However, if your horse is not fed a commercial feed and does not have access to pasture, he could likely benefit from more of this vitamin.

It’s important to note that horses can develop a toxicity with vitamin A if it is supplemented along with well-fortified commercial feeds.

Vitamin E

Vitamin E is considered the most important antioxidant for horses. Lush, green grass is plentiful in vitamin E, but estimates are that 30-80% of vitamin E is lost during the process of baling hay. Therefore, if your horse is on a hay-only diet, he will very likely need vitamin E supplementation.

All horses should get at least 1000-1500 IU of supplemental vitamin E per day if they are not on fresh pasture (although some nutritionists recommend as much as 2000-5000 IU per day). Vitamin E has been shown to be safe even when fed at higher levels, but too much of this vitamin may interfere with the uptake of other vitamins.

Because vitamin E is fat soluble, it should be provided with fat in the diet so it can be absorbed and utilized. Some commercial feeds contain added fat, but you can also feed a separate fat source in the form of flaxseed oil or rice bran. You will see vitamin E listed as alpha-tocopherol (this is the preferred form) on most supplements; it’s important to choose one from a natural source instead of a synthetic source since the horse will be able to better absorb it.

Trace Minerals

Zinc, copper, and selenium are all important antioxidants as well, and they are also commonly deficient in the equine diet. Selenium is a critical trace mineral, but can be toxic if over-supplemented. Check to see if your area’s soil is sufficient in selenium or have a blood test performed before supplementing. You can often find selenium added with Vitamin E in many supplements. 

Vitamin C (Ascorbic Acid)

Horses in good health can make their own vitamin C, so supplementation usually isn’t necessary. However, if a horse is stressed (from illness, heavy exercise, travel, etc.) supplemental vitamin C can be beneficial. Seven to ten grams of ascorbic acid per day short-term is usually recommended.


Derived from the microalgae, Haemotaococcus pluvialis, astaxanthin is a carotenoid, which means it can be converted into vitamin A by the body. Researchers have recently found that astaxanthin is a powerful antioxidant that can be extremely beneficial when supplemented to horses. 

In fact, studies have shown that this nutrient can significantly lower creatine kinase levels, a marker of muscle damage, in exercising horses. 

Oxidative Stress Supplements: Medical Muscle

Fullbucket’s Medical Muscle is a highly concentrated antioxidant formula that supports muscle recovery and endurance in hard-working horses. It contains astaxanthin, as well as L-Carnitine, and Vitamin E

This formula is 6,000 times stronger than Vitamin C. 

Medical Muscle can help support the following in horses:

  • Muscle and joint health by helping remove free radicals associated with exercise;
  • Energy and endurance;
  • Recovery after exercise;
  • Muscle, tendon and joint health;
  • Antioxidant protection;
  • Muscle support in horses that are at greater risk for tying up (rhabdomyolysis), muscle exertion, and stress from performance and training.

Mitochondrial oxidative stress occurs in all horses, but hard working horses are most susceptible to its effects. This is where antioxidant supplementation is important to keep them healthy and on top of their game. 

Highly Recommended: The veterinary-recommended super-antioxidant supplement designed to support your performance horse’s cellular health← 

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