There 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.