Things you HAVE to know about Vitamin E.

Of all the lines on the nutritional analysis you can find on the bags of feed you might have in your feed room one line, in particular, has come under quite a bit of attention in the last few years: vitamin E.

The last four or five years have seen some conclusive research on the importance of it and more importantly: how much our modern way of keeping horses has created a severe deficiency in a large number of them.

If you hate reading all the way down to get the key messages I will make it easy for you in this case:

Unless your horse is on lush pasture at least 12 hours a day for 6 months of the year there is a very high chance it is deficient in Vitamin E.

Why is vitamin E important?

I could tell you that it is an antioxidant and attempt to explain how it is involved in the healthy maintenance of almost all the tissue in your horses’ body as well as its immune system. I could tell you it is particularly important for the neuro-muscular system as well as the smooth running of numerous metabolical pathways.

But here are the take-home messages:

  1.  If your horse is deficient its muscles and nervous system are getting damaged a little bit every day and its immune system is also weakened.
  2. Except in very rare and tragic cases (Spinal degeneration or Neuroaxonal Dystrophy, Equine Degenerative Myeloencephalopathy, and  Equine Motor Neuron Disease), you cannot tell that your horse is deficient. There is no outward sign that something is amiss and yet in asymptomatic (we are all familiar with what that word means now don’t we??) animals, a biopsy of the muscles shows a very distinctive pathology.
  3.  If your horse/foal did not receive the appropriate amount of Vitamin E when it was growing up it is at increased risk of developing neurological issues.

Ok, the details:

Vitamin E is actually a group of compounds consisting of 2 subgroups: tocopherols (saturated) and tocotrienols (unsaturated). Within each subgroup, there are 4 individual isoforms (α, β, γ, and δ).  For mammals, only the tocopherols are of any importance. There are 8 different stereoisomers of α‐tocopherol alone and interestingly: only the RRR isomer is of any use to horses. So out of a large group compounds, we are only interested in a small fraction of them. I can see why the name Vitamin E caught on, however, much simpler 😉

Note for Breeders: Mares that have adequate tocopherol in their blood will produce colostrum that protects their foal better against infection. Another reason why broodmare in the last trimester should be supplemented if not on full pasture at that time.

Good pasture is particularly vital for broodmares and growing young horses.

Alpha-tocopherol is what is measured in horses’ blood and what provides us with the information to determine if the horse is deficient in “Vitamin E” or not.

So for now we will equate Vitamine E with alpha-tocopherol and continue on our merry way.

So what are the criteria for determining if a horse is deficient or not?

The amount of alpha-tocopherol is measured in their blood (the blood test costs roughly $200).

Horses deficient in Vit E can develop neurological issues.

If they have 4 microgram/ml of blood they are deemed sufficient

Between 2 and 4 micrograms, they are considered adequate but might be at risk of becoming deficient (depending on the time of the year) and their status.

At 2 micro-gram/ml they are considered marginal

Anything below 1.5 micrograms/ml is outright deficient whether there are any outward symptoms or not.

Levels as low as 0.3 to 0.8 microgram/ml were found in Przewalski horses kept in Zoo conditions and those animals suffered from spinal degeneration, unfortunately.

Vitamin E is found in fresh healthy grasses and forage of all sorts (between 45-400 IU/kg of Dry Matter).

If it’s green and grows out of the ground: it has vitamin E in it. Horses allowed to graze at least 12 hours a day generally absorb enough to cover their needs and even store some of the excesses.

Grazed down grass that’s been nibbled down to the nub, or mature grass that has turned yellow or that froze a few times don’t count. Also, it doesn’t do well with drying and heating, therefore it degrades very quickly in hay. Any hay that is a few months old has lost most of its Vitamine E.

This overgrazed pasture should NOT be considered a good source of Vitamin E for a horse.

The recommended dose of vitamin E is  900 to 1200 IU per day for a 1200lbs idle horse. Horses in work and broodmares need 3 to 4 times that amount (between 2000 to 4000 IU/day).

Thankfully Vitamine E is stored in fat so that horses can accumulate some in their liver and up to 90% in their fat reserve to have it available when it is no longer supplied by the grass. However, they deplete those reserves pretty fast. The higher their metabolic rate the quicker their reserves go down.

That means that horses that work for a living, broodmares, and particularly growing horses between the age of 5 months and 3 yrs old will need access to vitamin E during the winter month or risk becoming deficient.

Mature horses that are out on pasture all summer and worked lightly will probably be ok until the spring grass comes in once more. As demonstrated by this study done in 1994 on horses kept at pasture in Western Canada.

Seasonal variation in Vit E status in horses in Western Canada (Blakley and Bell, 1994)

A mature fat mare will be fine, a skinny gelding might not. An idle horse might do fine, a working one will likely need some supplement sooner rather then later. A pregnant mare will be ok until her last trimester at which point if she is not on pasture, or if the grass is not up yet, she will need to be supplemented. A young horse growing well will be fine for a few months but will then need to be supplemented, probably before the young grass starts to grow.

What does that mean for horses in boarding facilities that are fed hay year-round?


Or, for those with access to very grazed down pasture?


Or, those that can’t be on fresh grass for metabolic reasons?

Here is a case study.

All horses at this high-end boarding facility were fed good quality hay year-round regardless of turn-out arrangement and all horses had an individual feeding program where they were supplemented with a commercial ration fed at the recommended rate.

So why are horses that are being fed commercial feed fed at the right amount still deficient?

There are two things to consider.

Remember that I mentioned that Vitamin E is a group of compounds but only one form is actually useful to the horse?

Here is a breakdown of commercially available “Vitamin E” and how much of the useful form of vitamin E they actually contain:


From this chart we see that out of 1 mg of the d-alpha-tocopherol (RRR)-(the RRR refers to the specific isomer that is the one the horses metabolism can use fully-its the one found naturally in nature), the body gets 1.49 IU of vitamin E or roughly 1 mg so the full amount- it’s the best source of Vitamin E for horses-they can use it all.

But for 1 mg of the dl-alpha-tocopheryl acid succinate, the body gets only 0.89 IU or 0.4 mg of Vitamin E! So you would need to feed 2.3 to 3X the amount in order to get your horse the same amount as with the d-alpha-tocopherol.

All the compound that starts with dl- are synthetics and as you can see they are poorer overall in the useable form of the compound. They are however cheaper-much cheaper, but you need to feed more of it.

Commercial ration contains for the most part the synthetic version. So although the label says that you are feeding say 300IU/kg, because it is of a synthetic form (say: the dl-alfa-tocopherol acid succinate) you are actually only feeding your horse 60% of that in a form it can actually use. And when you consider that those numbers are the bare minimum you can see why most horses end up being deficient despite being fed “balanced” and “complete” ration.

The natural form and purest form of the vitamin, the one that is wholly useful to the horse (the alpha-tocopherol (RRR)) but this compound is fat-soluble and unstable (it reacts and changes). To turn this into a powder it needs to be changed to acetate form (sometimes called alpha-tocopherol acetate OR alpha-tocopheryl acetate)

As a result of these two facts, most feed and horse ration contain Vitamine E in the cheapest and least available form. Therefore if you are relying on the vitamin E contained in your horse ration to supplement your horse you are more than likely not providing him enough vitamin E because the amounts are the bare minimum recommended AND because it is not in a readily absorbed form.

What can be done?

Modern science and feed company thankfully seem to have a supplement for that.

Supplementing the horses with alfa-tocopherol is absolutely the way to go. National Research Center recommends between 1-2 IU/kg/day.

For a warmblood of 1200 lbs that means 900 to 1200 IU/day when fed at the recommended amount, most commercial feed I could find provide between 500 to 1200 IU of Vitamin E for a horse of roughly 1200 lbs. Those numbers are in line with the recommended amounts but they are the strict minimum and probably suited for horses that have access to grass at least part of the year and keep in mind they are likely synthetic forms of Vitamin E.

If your horse is kept on a dry lot and stabled at night you should probably supplement with a natural form of vitamin E above and beyond what is your horse’s ration, especially if it is in regular work- just read the label carefully and steer away from the dl-alfa-tocopheryl acid succinate or acetate.

The best practice is to supplement and then test levels a few months later.

Not all horses absorb Vitamin E at the same rate either (there seem to be slight differences between breed, age, and perhaps gender),  some might need to get a bit more-the only way to know is to test.

Also, keep in mind that because it is fat-soluble, it is better if it is fed along with some oil. So it’s important to up the fat content of the diet at the same time as the vitamin E.

For horses whose test show that they that require a rapid increase in their vitamin E level, there is really only one option: the d-alfa-tocopherol available in liquid form. This form of vitamin E has undergone a mechanical change to its properties to maximize its absorption (either by micellization or by nanodispersion-methods I won’t get into here but they are pretty neat!) – but it is not cheap.

As far as I could find there are only three products that offer this in North America.

Emcelle, Nano-E and Ellevate WS are the only liquid form of alpha-tocopherol (natural form) available in NA.


Bottom line: It’s really hard to replace good pasture. But unless your horse is living a quiet life out on pasture for at least 12 hours a day you need to supplement his diet with Vitamin E beyond what he might be getting in his ration. If it is not showing any ill effect you can feed him a powdered form of the Vitamine E, you just need to feed a bit more because, as we saw not all of it is readily absorbed but you can bring the tocopherol level in the blood up by feeding them.

However, if your horse is showing symptoms of vitamin E deficiency or needs to be supplemented quickly (like in the case of a broodmare that has been fed hay for most of its pregnancy) then the way to go is to use the liquid form (or water-soluble-as it is called form- because it is 6X more available to the horse metabolism).

If you are curious to know more I encourage you to check out the references below.

Also please share this so others can become aware: with the majority of horses being kept in boarding facilities where they have no access to grass, this is particularly relevant to them: even the best quality of hay will not provide them with the vitamin E they more than likely require.

As always I recommended that you work with a nutritionist to address your particular situation but hopefully this article as well as the others on this topic can help you ask the right questions.



For those that still have questions: below is a link to a conversation with Dr.Finno-  a leading expert in Vitamine E effect on horses

13:30-18:20 What are the different kinds of Vit E?
18:28-19:30 What are some whole food sources of Vit E?
19:45-22:30 Can supplementing Vit E reverse the effects of EDM?
22:45-24:15 Can Vit E be over supplemented?
24:20-27:12 How can one test for Vit E levels?
27:21-29:25 What levels are normal?
29:27-30:40 Can one supplement without testing first?
30:43-32:45 Vit E and Selenium what is the connection?
32:47-33:44 Can pastures be low in Vit E?
33:45-34:50 Should I test my feed source for Vit E?
34:53-36:26 Vit E for senior horses
36:30-37:33 Vit E and skin condition like rain rot
37:37-38:35 Cushing disease and Vit E
38:38-40:20 Focus on maintaining racehorses level of Vit E
40:25-41:51 Human Vit E supplements are they ok for horses?
41:55-43:30 Hoof and coat health and Vit E
43:34-44:05 Optimal blood concentration level of Vit E?
44:09-45:40 Is the Vit E in my horse’s food ration enough?
45:44-50:25 PSSM Type 1&2 and other muscle disorder and Vit E
50:29-52:04 Tying up in Racehorses is Vit E a solution
52:05-53:49 Foal dysphagia- link to Selenium and Vit E
53:54-55:35 How to transition from liquid Vit E to powder?
55:43-57:17 Vit E and weak or poor toplines in horses
57:21-58-03 How long does it take to get a horse to the right levels?
58:07-59:12 Effect of Vit E withdrawal in horses
59:15-1:00 Is Vit E a performance-enhancing substance?



Owner and worrier in chief at Formosus Sporthorses in Alberta she's been breeding horses for over 15 years. Warmblood, warmblood crosses, and a few saddlebreds. She loves handling mare and foals and is passionate about giving foals the best start possible.

1 Comment

  1. […] Number one your foal should have had access to good pasture for at the very least 12 to 14 hours a day. The key here is that horses are designed to eat grass, lots of it and there are things in grass that simply can’t be found in rations. Mainly vitamin E and beta-carotene. More about vitamin E here: What you need to know about vitamin E. […]


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