Antioxidants for Horses

A recent discussion on The Naturally Healthy Horse’s facebook page prompted the idea to write this post. We were discussing which horses should be supplemented with vitamin E and that got me thinking about antioxidants for horses in general. I wrote an article a couple of years ago, Antioxidant Status in Three Day Eventing Horses Studied, in which I learned quite a bit about the topic.

Oxidation is a natural process that occurs when oxygen is combined with various other elements in the body during metabolism.  The rate of oxidation depends on the activity of the animal.  At rest, the rate of oxidation 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.  Oxidative stress causes the amount of free radicals (damaged cells missing a critical molecule  and on a ‘rampage’ to pair with another molecule) to increase.  An overabundance of free radicals will damage healthy cells, which can easily lead to decreased immune function, illness, or nervous system dysfunction within the animal.  (e.g.–Cushing’s disease/ PPID is linked with oxidative stress.)

This is very antioxidants come into play.  Antioxidants are substances such as vitamins, minerals, plant extracts, etc. that help slow down and prevent damage from free radicals.  They are a crucial part a horse’s (or any animal’s) diet.

So you may be wondering how you can provide antioxidants in your horse’s diet.  The good news is that if your horse is on green pasture, he is likely getting plenty of antioxidants.   But many horses today do not (or can not) have access to green pasture.  And the process of drying and curing hay destroys the  most of the antioxidants present within the plants.  This is when antioxidant supplementation is necessary.

And it’s also possible that some horses need more antioxidants than what their pasture can provide, such as in these cases:

  • Horses in moderate to heavy work;
  • 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 according to this article from Horse Journal, “The basics of sound antioxidant nutrition are a provision of an adequate intake of vitamin E, vitamin A, and trace minerals (copper, zinc, selenium, iodine, etc.)”


Vitamin A (Retinol)

Green grass and most commercial feeds are plentiful in vitamin A.   Fresh hays contain some vitamin A as well (vitamin A decreases the longer hay is stored).  But if your horse is not fed commercial feeds and does not have access to pasture, it’s possible that he could benefit from more vitamin A.

Carrots (and other yellow/ orange vegetables) contain beta-carotene which is a precursor to vitamin A (meaning the body can convert it to vitamin A) so they are always a healthy treat.

Here are the NRC recommended requirements for vitamin A:

  • 15,000 IU per day for maintenance horses
  • 22,500 IU per day for moderately active horses
  • 30,000 IU per day for pregnant/lactating mares

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.   So 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 shown to be safe even when fed at higher levels, but too much of it can interfere with the uptake of other vitamins, so again, don’t overdo it.

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 oil or rice bran.  You will see vitamin E listed as alpha-tocopherol (this is the preferred form) on most supplements–choose one from a natural source instead of a synthetic source since the horse will be able to better absorb it.

This is a wonderful article with comparing several different forms of vitamin E for horses.


Trace Minerals

Zinc, copper, and selenium are the most commonly deficient trace minerals in horses’ diets–and all important antioxidants.  You won’t know how much zinc and copper to supplement unless you test your hay (and look at feed labels), but it’s a pretty good guess that your horse needs more if you aren’t already supplementing it.  I feed these minerals individually (from Horsetech), but you can find them in mineral mixes as well (I strongly recommend finding one that doesn’t have iron!)

Selenium is a critical trace mineral, but one you must be careful about as it can be toxic if over-supplemented.  Check to see if your area’s soil is sufficient in selenium (see this post for more information) or have a blood test performed before supplementing selenium.  If it is needed, you can often find selenium added with Vitamin E in many supplements.


Vitamin C (ascorbic acid)

Horses in good health can synthesize (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.  7-10 grams of ascorbic acid per day short-term is usually recommended.




Vitamin Function

Antioxidants Fight Bad-Boy Free Radicals in Horses

Vitamin E Supplementation for Neurologic Disorders

Nutritional Horse Supplements: Antioxidant Overview

Antioxidants and Your Horse

Vitamin A for Horses


Hi! My name is Casie Bazay. I'm a mom, a freelance writer, and a certified equine acupressure practitioner.

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2 Responses

  1. Lea says:

    That is why I LOVE supplementing with herbs because many of them are high in these vitamins. Calendula, dandelion, nettle, and kelp are high in Vitamin A. Rosehips, nettles, kelp, and dandelion are high in Vitamin C and kelp is high in Vitamin E and contains zinc.

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