EPM, Folic Acid and Birth Defects

By By Christine Barakat

An Ohio State University researcher has found a possible link between folic acid supplementation and fatal deformities in the foals of mares who are undergoing treatment for equine protozoal myeloencephalitis (EPM). In reviewing the cases of three foals born to mares receiving both EPM treatment and supplemental folic acid, researcher Ramiro Toribio, MS, found that the foals all suffered from severe kidney defects and underdeveloped bone marrow. None of the youngsters survived more than two weeks.

EPM, an inflammation of the brain and spinal cord caused by protozoal infection, is usually treated with a combination of two drugs. One of them, pyrimethamine, is known to inhibit the body’s ability to utilize folic acid. As a result, owners of EPM-affected mares often give their horses the vitamin as a supplement, says Toribio.

"On the surface, it makes sense to supplement [these mares] with folic acid because the drug used causes those levels to drop," he says, "but it appears that, paradoxically, folic acid supplementation may actually make the problem worse."

Folic acid has an active and inactive form, Toribio explains. The active form is readily available through the diet and can be utilized immediately by the body, but the inactive form, which is given as an oral supplement, must be activated by the horse's liver before the body can use it. "We think that pyrimethamine interferes with this conversion process," Toribio says, "and actually makes the active and inactive folic acid compete against each other so there is less absorption of both." The result is counterintuitive: Giving extra folic acid to a mare being treated for EPM may actually reduce the amount of folic acid available to her.

Toribio says it is not known how the combination of supplementation and medication leads to folic acid deficiency. He cautions that his findings are based on a small number of horses and that more research is needed. "But I would certainly recommend not giving folic acid supplementation to a mare being treated for EPM until we know more," he says.

This article is from EQUUS Magazine, Issue 248 (June 1998), copyright 1998 by PRIMEDIA Enthusiast Publications, Inc. All rights reserved.

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