Horses with clinical signs of equine motor neuron 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|
|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.