Vitamin E

Vitamin E is not one compound but eight: four tocopherols and four tocotrienols. The one that matters biologically in animals is alpha-tocopherol, and it works as the body's main fat-soluble antioxidant, sitting inside cell membranes and intercepting the free radicals that would otherwise start a chain reaction of lipid peroxidation. Muscle, nerve and immune cells are the tissues that suffer first when it runs short.

This entry is weighted towards horses, because horses are where vitamin E deficiency is a real, common and sometimes catastrophic clinical problem — while in dogs and cats on complete commercial diets it is mostly a non-issue.

Natural Versus Synthetic: the Thing Most Labels Obscure

This distinction is worth more than the milligram count, and it is the single most useful thing on this page.

• Natural vitamin E is d-alpha-tocopherol, sometimes written RRR-alpha-tocopherol. It is a single stereoisomer, the one the body's transport proteins recognise.

• Synthetic vitamin E is dl-alpha-tocopherol, also written all-rac-alpha-tocopherol. It is a mixture of eight stereoisomers, only one of which is the natural form.

The natural form is roughly twice as bioavailable. In horses the gap is wider still in practice, because the form that actually raises blood levels reliably is water-dispersible natural alpha-tocopherol — a micellised liquid. Powdered synthetic vitamin E fed to a deficient horse frequently fails to move serum values at all, which is how owners end up supplementing for months with nothing to show for it. If you are treating a deficiency, the form is not a detail.

Horses: Where Deficiency Really Happens

Fresh green pasture is rich in vitamin E. Hay is not — the vitamin degrades substantially during curing and continues to fall in storage, so hay cut months ago may retain very little. A horse with no grazing, living on stored forage, is a horse at genuine risk. Dry lots, winter, drought, stall rest and heavily worked horses on hay all point the same way.

The deficiency diseases are specific and serious:

• Equine motor neuron disease, in which motor neurons degenerate, producing muscle wasting, trembling, weight shifting and a characteristic low head carriage.

• Equine degenerative myeloencephalopathy, a spinal cord disease of young horses causing ataxia and incoordination.

• Vitamin E deficient myopathy, presenting as weakness and muscle atrophy without the dramatic enzyme rises of other muscle diseases.

The National Research Council figure for maintenance is around 1 to 2 IU per kilogram of body weight daily, so roughly 500 to 1,000 IU for a 500 kg horse. Horses being treated for deficiency or neurological disease are commonly given far more, in the range of 5,000 to 10,000 IU daily of the natural water-dispersible form, under veterinary direction. Serum alpha-tocopherol can be measured, which means you do not have to guess — and given how often synthetic powders fail, retesting is how you confirm the supplement is working.

Foals, Broodmares and Working Horses

Foals start life with low reserves. Mad Barn notes that vitamin E is not transferred through the placenta, so a foal depends on colostrum and milk — which is why the mare’s intake in late pregnancy and lactation matters. Mad Barn puts pregnant and lactating mares, and working horses, at a minimum of 1,000 IU a day, weanlings and yearlings at 500 to 750 IU, and horses on pasture at roughly 2,000 IU a day from grass alone.

Two conditions show up in young horses:

• Equine neuroaxonal dystrophy and degenerative myeloencephalopathy (eNAD/EDM) — abnormal gait, dullness and a reduced menace response, typically appearing between 6 and 12 months of age. UC Davis notes that whether disease develops depends on the age at which deficiency starts, how long it lasts, the individual’s genetics and other dietary factors, so foals from affected lines deserve particular attention.

• Nutritional myodegeneration, or white muscle disease — linked to combined vitamin E and selenium deficiency, and seen as weak, stiff, painful muscles, difficulty swallowing and laboured breathing. This is a veterinary emergency in a foal.

By contrast, equine motor neuron disease in adults generally follows a long deficient diet — Mad Barn cites at least 18 months — which is why the hay-fed horse with no grazing is the classic case.

Testing Your Horse: the Numbers

A blood sample for serum or plasma alpha-tocopherol is the most readily available test, according to the UC Davis Finno Laboratory, which researches vitamin E related neurological disease in horses. Their reference is simple: above 2 µg/mL is adequate, below 2 µg/mL is deficient. Mad Barn’s nutritionists use a finer scale — 1.5 to 2 µg/mL marginal, under 1.5 deficient — and describe 4 to 6 µg/mL or higher as optimal, a range typical of horses on good grazing.

• Get a baseline before you start. SmartPak recommends testing first, then retesting about two weeks after starting a supplement.

• Samples need careful handling. Alpha-tocopherol degrades, and labs use special protocols to protect the sample, so ask your vet how theirs wants it collected and shipped.

• No rise on retest usually means the form, not the dose. That is when switching to a natural water-dispersible product, as described above, makes the difference.

Selenium Belongs in This Conversation

Vitamin E and selenium work together in the antioxidant system, and selenium is deficient in the soil across large parts of the world. They are often supplemented as a pair. But they are not equally forgiving: selenium has a narrow margin between adequate and toxic, and selenium toxicity in horses causes hoof wall separation, hair loss and worse. Vitamin E has a wide safety margin. Supplement vitamin E freely within reason; supplement selenium only on the basis of testing and veterinary advice.

How Much Is Too Much

Vitamin E is forgiving, but it has a ceiling. UC Davis gives the upper safe level as 20 IU per kilogram of body weight — about 10,000 IU a day for a 500 kg horse, the top of the treatment range in our table. Above it, coagulopathy and impaired bone mineralisation have been reported, and very high supplementation may impair absorption of other nutrients; Mad Barn specifically flags vitamin A.

UC Davis also suggests that a healthy horse already getting adequate vitamin E from its diet needs no more than about 500 IU a day in supplement form. The large doses belong to deficient or neurological horses, with testing to guide them — not to every horse as insurance.

Dogs and Cats

Deficiency is uncommon in animals eating a complete commercial diet, which is required to contain vitamin E. Two situations change that:

High polyunsaturated fat intake raises the requirement. This is the most practically relevant point for our customers. Polyunsaturated fatty acids are exactly the molecules vitamin E protects from oxidation, so the more of them in the diet, the more vitamin E is consumed doing that job. An animal on a generous fish oil or krill oil regimen has a higher vitamin E need than one that is not, which is why well-formulated omega-3 products include it.

Feline steatitis is the classic illustration. Cats fed diets heavy in oily fish without adequate vitamin E develop inflammation of body fat, historically called yellow fat disease — painful, and entirely a consequence of the vitamin E to polyunsaturated fat ratio. It is rare now precisely because commercial diets account for it. See cat safety for more on feline particulars.

Beyond that, vitamin E is used in dogs for skin and coat condition, and appears alongside silybin and phosphatidylcholine in the veterinary liver products discussed in our milk thistle entry.

How Much to Give

Animal · Typical daily amount

• Cat — 30 to 100 IU

• Dog under 20 lbs — 100 to 200 IU

• Dog 20 to 50 lbs — 200 to 400 IU

• Dog 50 to 90 lbs — 400 to 600 IU

• Dog over 90 lbs — 600 to 800 IU

• Horse, maintenance — 500 to 1,000 IU

• Horse, deficient or neurological — 5,000 to 10,000 IU, vet-directed

How to Give It

Vitamin E is fat-soluble, so give it with a meal that contains fat — on an empty stomach much of it goes unabsorbed. This is the same principle that applies to hemp oil, and it means the two go together conveniently. For horses, liquid water-dispersible product goes onto feed; for dogs and cats, a capsule can be pierced and squeezed onto food. Improvement in coat condition takes weeks; serum levels in a deficient horse typically shift within a few weeks on an adequate product.

What to Look For When Buying

• "d-alpha-tocopherol" on the label, not "dl-alpha-tocopherol." One letter, roughly double the potency.

• Water-dispersible or micellised for horses being treated for deficiency.

• IU stated per scoop or capsule, and mixed tocopherols if you want the fuller profile.

• Check whether selenium is included, and do not stack two selenium-containing products.

• Opaque packaging and a date. Vitamin E oxidises, which is faintly ironic for an antioxidant. Our shelf life entry covers storage, and our own lab results exist for the same reason: a label you cannot verify is a number you cannot trust.

Side Effects and Cautions

• Bleeding risk at high doses. Vitamin E interferes with vitamin K dependent clotting. This matters before surgery, and alongside anticoagulants or high-dose fish oil. Tell your vet before any procedure.

• It accumulates. Being fat-soluble, excess is stored rather than excreted, so more is not better indefinitely.

• Digestive upset at high amounts.

• Selenium confusion — the most likely way to do harm here is by inadvertently double-dosing selenium from a combination product.

• Human capsules may contain soybean oil or additives; check for xylitol in any chewable or gummy format.

When to Talk to Your Veterinarian

For horses: any trembling, muscle wasting, weakness, incoordination, unexplained weight loss or a low head carriage warrants a call, and serum alpha-tocopherol should be part of the workup. Before surgery in any species, disclose vitamin E. And before adding selenium to anything, get testing first — that is the component with a real toxicity ceiling.

How It Fits With Hemp

There is a direct and practical relationship here rather than a marketing one. Our products are oil-based, which means they are made of exactly the kind of fats vitamin E protects. Vitamin E is widely used as a natural antioxidant in oil formulations for that reason, and an animal on a fat-rich supplement regimen has a modestly higher vitamin E requirement than one that is not — most relevant if you are also feeding fish oil.

It also works the other way round: because both vitamin E and cannabinoids need dietary fat to absorb properly, giving them in the same meal is efficient. Our serving guide covers amounts, and for horses the 5,000mg olive oil concentration in our equine range is the practical choice at equine body weight — see our equine research for what we have studied.

Frequently Asked Questions

Do horses on hay need vitamin E? Very often yes. Fresh grass is rich in it and hay loses much of it during curing and storage, so a horse with no grazing is at real risk. Around 500 to 1,000 IU daily covers maintenance for a 500 kg horse.

Is natural vitamin E better than synthetic for horses? Substantially. Natural d-alpha-tocopherol is roughly twice as bioavailable, and water-dispersible natural forms raise blood levels far more reliably than powdered synthetic ones, which often fail to move serum values at all.

How much vitamin E can I give my dog? Commonly 200 to 400 IU daily for a mid-sized dog, up to 800 IU for a large one, always with a fatty meal. Most dogs on complete diets are not deficient.

Can you give too much vitamin E? It has a wide margin, but it is fat-soluble and accumulates, and high doses interfere with vitamin K dependent clotting. Disclose it before surgery and avoid stacking it with anticoagulants.

Should I give vitamin E with selenium? They work together, but selenium has a narrow toxic margin while vitamin E does not. Test before supplementing selenium, and never run two selenium-containing products at once.

Does fish oil increase vitamin E needs? Yes. Polyunsaturated fats are what vitamin E protects from oxidation, so a diet high in them consumes more of it. Well-formulated omega-3 products include vitamin E for this reason.

For the equine side, the University of Minnesota's equine programme publishes practical material on vitamins for horses. For the underlying nutrient science across species, the National Academies' Nutrient Requirements of Horses is the reference standard.

Does a horse on good pasture need vitamin E?

Often not much. Fresh grass supplies roughly 2,000 IU a day, and UC Davis suggests no more than about 500 IU of supplement for a horse whose intake is already adequate. A serum test settles it.

Why is vitamin E important for foals?

Very little crosses the placenta, so foals rely on colostrum and milk. Deficiency in young horses is linked to eNAD/EDM and, with selenium deficiency, white muscle disease.

What are the signs of vitamin E deficiency in dogs?

It is rare on complete diets. The Pet Food Institute lists muscle weakness and reproductive failure in dogs, and muscle weakness and poor appetite in cats; eye problems are also reported.

Can my dog take vitamin E during chemotherapy?

Ask your oncologist first. Vitamin E can interact with some chemotherapy drugs, anticoagulants and anti-platelet medication, and whether antioxidants help or hinder during cancer treatment is still debated.

Which foods contain vitamin E for dogs?

Plant oils such as sunflower, safflower and wheat germ oil, leafy greens, eggs and fish such as salmon. Complete commercial foods add it as alpha-tocopherol.