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vitamineThere are some things to consider when supplementing and testing  vitamin E levels in horses.  Why do it?   The need for supplementation probably stems from deficiencies that are associated with degenerative myeloencephalopathy, equine motor neuron disease, vitamin E-deficient myopathy, and nutritional myodegeneration—or a diagnosis of EPM (unproven).

You decided to test instead of supplementing because conditions that warrant supplementation are rare, supplements are  expensive, and over supplementation may not be benign.  There are high-performance liquid chromatography tests that are as expensive as they sound. There are also enzyme linked immunosorbent assays that are used to capture vitamin E (alpha-tocopherol) from body fluids.  The when and how samples are collected and handled are important to obtain accurate values from ELISA testing. There is a study funded by Kentucky Performance Products, KPP--the makers of Elevate, that determined the effects of feeding different formulations of their products on serum, CSF (cerebrospinal fluid) and muscle tissues.  They used liquid chromatography methods.

It is necessary to test to find out if the horse has a deficiency. How do you test for vitamin E in serum? When using the more common ELISA test on serum, the collected blood should be allowed to clot for 10-20 minutes at room temperature and then removed from the tube carefully without transferring any sediments.  The serum should be protected from light during storage or transport to the lab. When plasma is used, the sample should be collected in an EDTA or sodium citrate tube.  The plasma should be removed from the cells within 30 minutes and no sediment should be removed with the plasma. Samples should be tested within 5 days, stored cold., and protected from light.  Samples stored frozen can be tested within one month.  If samples are stored at –80 the test can be used within 60 days.  Hemolysis will change the results of the vitamin E test.   The time of feeding vitamin E, the horses diet, and other supplements that are added to the diet can affect the bioavailability of  vitamin E and its detection in body fluids.

Horses get natural vitamin E from green forage.  Horses that are confined to a stall or they are required to abstain from fresh grass, are at an increased risk to develop deficiencies.  The normal value of vitamin E in the horse is > 2 micrograms/ml.  A value less than 2 micrograms/ml would mean the horse was deficient in vitamin E. There is no information available for over supplementation and the effects of vitamin E toxicity in horses. Horses show individual variation in the ability to absorb vitamin E from supplements.

The bioavailability of vitamin E when supplemented is important.  Natural vitamin E is composed of one stereoisomer while synthetic vitamin E has several isomers, of these isomers only one is readily available to the horse. If the neurological disease is due to a deficiency of vitamin E in the central nervous system the synthetic acetate form of vitamin E has no impact on the CSF levels according to KPP. The KPP study claims the micellized water-dispensable form, a liquid, is as much as 6 times more bioavailable than other synthetic forms and allows a rapid rise in serum concentrations within 12 hours.  Levels of 10,000 IU/day can increase CSF levels within 2 weeks.  Likewise, serum levels decline rapidly after discontinuing supplementation.

The bottom line for supplementation is that horses without clinical signs of deficiency can be supplemented with a synthetic form at 10 IU/kg body weight per day and serum levels are expected to  increase after 47 days or so.

If neurological disease is present, a diagnosis of equine motor neuron disease or vitamin E deficient myopathy (diseases that are responsive to supplementation), are expected to respond to vitamin E.  A regime of supplementation of 5000 to 10,000 IU vitamin E given daily is the standard protocol.  Remember, the water dispersible form is more appropriate for these conditions when it is desirable to increase levels quickly.  There is a rapid decline in serum values when horses are removed from some forms of vitamin E supplementation and a tapering regime may be appropriate. Another point is that there is no correlation between serum and muscle levels of vitamin E. If the disease is vitamin E-deficient myopathy an alternate protocol may be required.

To summarize, if a horse is suspected of a low vitamin E level due to disease or diet, the serum and/or CSF should be tested.  The normal vitamin E value is >2 micrograms per ml of serum.  Abnormal values will be returned if the sample wasn’t collected and handled properly or if the sample was held too long, even if it was frozen. Light is detrimental to vitamin E in the serum and in supplements, samples need to be protected from inactivation as soon as they are collected.  Samples that contain microparticles or are hemolyzed will give an abnormal value.  It is important to select the most appropriate dose and formulation to achieve normal and sustained values when supplementing.  The rate of decline in the serum may depend on the form of the supplement that is given. And finally, there is an individual variation in the response to supplements so individual protocol should be designed to achieve a therapeutic response.

Horses with clinical signs of equine motor neuronprzewalski-1972728__340 disease (EMD) or vitamin E deficient myopathy require supplementation with vitamin E.  Horses that graze green grass should be fine without supplementation.  Supplements are expensive, here is a primer to guide you.

The critical factors associated with vitamin E are: determining that your horse is deficient (solution: test the serum levels); deciding what supplement is most appropriate (solution: determine what are you treating); delivering the dose efficiently to the horse (formulation and dose); and when to discontinue treatment (test the serum levels!)

Supplementing with the intention to increase vitamin E in the central nervous system (CNS) of a horse with neurologic disease requires a different protocol than supplementing for diet deficiency in a normal horse (a horse that has no access to green grass).  Studies show that some supplements do not increase the levels of vitamin E in brain tissue.  Studies show that vitamin E supplements do not increase the levels of the vitamin in muscle tissue.  And some supplements are active at five to six times other formulations!

There are no studies describing toxicity in horses from too much supplementation.  Vitamin E can be toxic because it is stored in fat (lipid) and is not excreted like water soluble vitamins are. It is possible that vitamin E inhibits vitamin A, another fat soluble vitamin although there are no published studies. In other animals, including humans, neurologic complications result from overdosing vitamin E!  There is no reason to suggest toxicity won’t occur in horses.

Horses showing no clinical signs of vitamin E deficiency

Supplementing with vitamin E can be expensive and can put a horse at risk for toxicity. If you suspect a deficiency you can easily test the serum concentration.  Samples need special handling, you must keep the plasma (purple top tube) chilled and protected from light.  Send it to your diagnostic laboratory on ice overnight.

Is it time to stop supplementing?  A simple test will tell you.  Because there is a rapid decline of serum levels after discontinuing some forms of vitamin E, it is best to wait a week after stopping vitamin E dosing before sending a serum sample for testing a long time supplemented horse.

Clinically ill horses

Horses showing clinical signs of equine motor neuron (EMD) disease or vitamin E-deficient myopathy can benefit from treatment.  Often suggested, but not proven, vitamin E is supplemented in  cases of active equine protozoal myeloencephalitis (EPM), with or without measured low levels.

Determine the base line levels of serum vitamin E before supplementing.  In diseased horses requiring supplementation, 5000 IU/day of a soluble, natural form is useful.  Not all horses respond the same way to supplements- there is individual variation!  After two weeks of supplementing the serum level should be assessed and adjust the dose accordingly.  A tapered regime with a gradual transition to a natural powder form of vitamin E is  appropriate.  The natural power form of vitamin E will return a horse to a normal serum value in 7 weeks but  normal CSF levels are not achieved with this supplement-form.

Levels of vitamin E

Normal serum levels of vitamin E in horses are greater than 2.5 µg/ml.  A level that is considered adequate is a range between 1.5-2.4 µg/ml.  Horses with serum levels less than 1.5 µg/ml are deficient.

Normal levels decline significantly in just 18 days in horses that are not allowed access to grass and are fed a pelleted ration that is not supplemented.  Considerations here are horses stalled due to colic surgery, metabolic syndrome, or other similar conditions.  Horses don’t have green grass in northern climates during the winter, something to consider.

Vitamin E levels in serum
Normal 2.5 µg/ml
Adequate 1.5-2.4 µg/ml
Deficient less than 1.5 µg/ml

It is interesting to note that in a controlled study there were no differences in the mean concentration of CSF vitamin E in un-supplemented (normal levels were present) or supplemented horses (all supplements).  Or in deficient horses, before and after supplementation!  There was a significant (linear) correlation between serum and CSF concentrations, the higher the serum level the higher the vitamin E in the CSF of most horses.  It is possible there is a limit to the amount of vitamin E that can be measured in the CSF (does it all go to the cell membranes) or it is a fault in the testing protocol (little correlation of values with test results).

Types of supplements

Vitamin E is available as an injection, usually in conjunction with selenium, and is a form that is by prescription for use by a licensed veterinarian.  Some serious and life threatening reactions can occur with intravenous or intramuscular injections of vitamin E-selenium.  The injectable form bypasses the inhibition seen in some oral formulations. Oral synthetic and natural vitamin E preparations are available.  The synthetic has eight stereoisomers (the molecular shape of the molecule and its rotation).  Animals have a preference for only one.  Natural vitamin E comes in only one isomer, the one preferred by the liver.  There are two synthetic forms of acetate, the powder is twice as available to the animal as the pelleted form, the powder increasing serum concentrations in about two months.  The water soluble, liquid form, is five to six times as available for uptake by the horse and increased concentrations are accomplished in 12 hours.  Thus the acetate forms elicit a gradual increase when supplemented.

What?  Who said sulfur inhibits vitamin E?

Vitamin E and selenium are intertwined with sulfur metabolism.  There is a relationship between selenium and vitamin E overcoming sulfur-induced depletion in the body.

What the vitamin E Guru’s suggest

Horses that have no clinical signs of deficiency can be supplemented with the less expensive acetate forms at 10 IU/kg body weight per day over months to achieve normal serum vitamin E levels.

The acetate form isn’t a good choice in horses with clinical signs of EMD or vitamin E deficient myopathy.  These horses require an immediate increase in serum and CSF vitamin E concentrations.  The veterinarian can use an injection to rapidly increase levels and the treatment can be repeated at 5-10 day intervals.  This form is labeled for selenium-tocopherol deficiency syndrome that presents clinically as rapid respiration, profuse sweating, muscle spasms and stiffness accompanied by an increased SGOT (liver enzyme).

Levels can be restored to normal by giving 5000 IU/day of the soluble vitamin E and then tapering the regime to transition to 5000 IU/day of the oral acetate. This protocol resulted in horses with a prolonged increase in CSF concentrations 8 weeks after beginning supplementation.

Sulfur in the digestive track can inhibit vitamin E uptake, in sulfur-inhibition resulting in deficiency, an injectable form is preferable.

What we suggest

Test the serum  vitamin E levels before supplementing this essential nutrient and again after 7 weeks of supplementation. After 7 or more weeks, discontinue the supplement for 7 days and then test.  It may be wise to re-evaluate serum vitamin E levels after several weeks on the acetate form to ensure concentrations remain within a normal range. It may be of value to determine vitamin E levels in horses suspected of EPM.  A diagnosis of the neurologic disease EMD can be supported by measuring a low serum vitamin E concentration.  Test these horses when they are tested for suspected EPM and once on therapy, 7 weeks later.  Horses with equine degenerative myeloencephalopathy (EDM) will not respond to vitamin E.  EDM is an inherited condition that prevents uptake of vitamin E early in life.  Once neurological signs are present they usually don’t get worse…or better in these EDM horses.

Vit EFat soluble vitamins are important in equine nutrition, vitamins in this group are M, A, D, and E.  Fat soluble vitamins are important in cell membrane functions and immunity.  Vitamin E, also called alpha-tocopherol,  is unique because it isn’t involved in specific metabolic functions but it is the body’s major fat soluble antioxidant.  The action of the anti-oxidant vitamin is to prevent free radicals from destroying (though oxidation) fats in the body.

Vitamin E  is found in green grass, horses that are on pasture will get plenty of vitamin E in their diet. Because horses don’t make this vitamin it is called an essential daily nutrient.  Horses that may need supplementation include pregnant mares, mares with foals, young growing horses, and performance horses that do not have access to green pastures. Horses that are restricted from eating lush grass, horses with metabolic syndrome, are also at risk for inadequate levels. Vitamin E is a treatment for Equine Motor Neuron Disease (EMD) but has no effect in horses with Equine Degenerative Myeloencephalopathy (EDM).  Vitamin E is often suggested to enhance recovery of horses with Equine Protozoal Myeloencephalitis (EPM) although there are no studies to support this recommendation. You can read a little more about these rare diseases, EMD/EDM/EPM at

There are no cost-effective means of rapidly increasing serum and cerebrospinal fluid levels of alpha-tocopherol and then sustaining the concentrations; a recent report recommends a water-dispersible formulation followed by a gradual transition to the acetate form of Vitamin E over a 7 week period. This study also highlights the need for periodic evaluation of Vitamin E concentrations because responses vary among individuals.  There are plenty of reviews of supplements and amounts to use in each type of deficiency; the need for supplementation should be discussed with your veterinarian. Remember, supplements are not without risk, especially supplementing fat soluble vitamins. How much is too much and what does Vitamin E toxicity look like? In people an overdose can cause muscular weakness, fatigue, diarrhea and bleeding.  The possibility of bleeding is of the most concern in supplemented horses.

The good news is that Vitamin E is easily  measured in the blood.  The alpha-tocopherol levels are reported as micrograms per ml (µg/ml).  If a horse has more than 2 µg/ml the level is adequate.  If the range is between 1.5 –2 µg/ml the levels are marginal and if the levels are less than 1.5 µg/ml the horse is deficient. A blood level should be taken before supplementation, after 30 days and prior to discontinuing therapy.  If desired levels aren’t attained after 30 days a different formulation may work. Testing is less expensive that maintaining a horse on a needless supplement or overdosing a horse.

2 µg/ml Adequate, no supplementation needed
1.5 –2 µg/ml Marginal
<1.5 µg/ml Deficient

Pathogenes no longer offers testing Vitamin E levels in serum and CSF.