Tests of the medication domperidone indicate it is effective against equine fescue toxicosisEquine fescue toxicosis can now be prevented by daily administration of a medication called domperidone for the last 15 days before foaling, according to a study conducted by D. L. Cross, Ph.D. at Clemson University in Clemson, South Carolina.

Equine fescue toxicosis is caused by ingestion of an endophytic fungus, acremonium coenophialum, which contaminates tall fescue forage and seed. Mares in their last month of gestation are most susceptible to the toxicity, which produces prolonged gestation, lack of or low milk production, dystocia (difficult birth), malpresentation of the fetus, premature placental separation (red bagging), tough and thickened placentas, weak and immature or abnormal foals, and foal and mare mortality.

Tall fescue is a cool season, perennial grass prevalent in the eastern and central United States. A high incidence of equine fescue toxicosis has been found in Kentucky, Virginia, South Carolina, Florida, Arkansas, Missouri, Colorado, and California. Warm winter temperatures and the application of nitrogen fertilizer to contaminated pastures increase the severity of the toxicity.

In areas where equine fescue toxicosis is endemic, the only preventive has been to remove the broodmare from pasture containing contaminated tall fescue 30 days in advance of her foaling date. This means confining the mare to a dry lot or a stall, which, in most cases, is impractical.

Under Cross's study, domperidone treatment is begun within 15 days of the mare's expected foaling date if she is to be left on tall fescue, and ten days if she is to be removed from the contaminated pasture. It is administered like a paste dewormer: 4 ccs-to-6 ccs (depending upon the mare's weight) of a brown, molasses-based slurry given by oral syringe. Mares which are agalactic, i.e., lack milk production, can also be treated with domperidone even if they are not suffering from equine fescue toxicosis. The study has shown that a high percentage of mares began producing sufficient milk when domperidone treatment was started at or near foaling and continued for five to ten days.

Scott Pierce, D.V.M., of Rood and Riddle Equine Hospital in Lexington, Kentucky, has been working with Clemson University on the domperidone study. Pierce reports that a several farms in the Lexington area are participating in the study. "One of the farms," Pierce said, "had a known history of problems with fescue. Since using domperidone, all of their problems have been alleviated." In the past two years, Pierce has not seen a single case identifiable as equine fescue toxicosis in any of the broodmares receiving domperidone under his supervision. He concluded, "I have found it to be highly effective. There is something to it. It does work."



How it works

Here is how it works: The ergot alkaloids in the endophyte fungus tie up the dopamine receptors throughout the mare's body and mimic dopamine. Dopamine is a biochemical that naturally occurs throughout the body and affects the function of various glands, organs, muscles, and nerves. In mares, an excess of dopamine or the ergot alkaloids decreases the production of prolactin and progesterone. Prolactin is a hormone secreted by the pituitary gland, which stimulates milk production. Progesterone is a gonadotropic hormone, which maintains a healthy, normal pregnancy. Domperidone blocks the dopamine receptors, essentially decreasing the interaction of the ergot alkaloids with these receptors and preventing the reproductive problems, the cause. Unlike other dopamine antagonists, domperidone does not cross the blood-brain barrier to cause central nervous system side effects, such as nervousness or lethargy.

Domperidone originally was used in dogs to control vomiting. In countries other than the United States, it is approved for human use to control vomiting associated, for instance, with chemotherapy. Based on feedback from his study participants, Cross believes domperidone is harmless and essentially free from adverse side effects. The only "side effect" he said he has witnessed is milk production in barren mares who were given the drug during some of the early testing. "And that's exactly why we use it in agalactic mares," Cross said. He does warn, however, that kits that test the mare's milk to predict imminent foaling will register a false positive for mares receiving domperidone.

Cross first began investigating the equine fescue toxicosis problem 12 years ago. Following many years of testing and development at Clemson University, he obtained a U.S. patent for his specific application of domperidone in the treatment of "fescued" animals. Through a joint venture between Cross and Clemson University's Center for Applied Technology, Cross now produces the drug through his company, Equi-Tox Inc.



Compassionate use

The food and Drug Administration is considering bestowing "compassionate use status" on domperidone in 1997, which means the medication would be approved for limited use to treat severe maladies for which animals would suffer if the medication were not available. Under this status, only those veterinarians working with Clemson University and Cross at the time the status is granted will be permitted to use the drug. New users will need to obtain specific FDA approval to participate in the study.

Although it sounds like an expensive champagne, domperidone costs only about $7 per day and is required for a minimum of 15 days. Since administration is begun 15 days prior to the mare's expected foaling date, if the mare goes beyond her due date those additional days must be added to the calculation. In extreme cases in which the mare gestates for a full year, domperidone may be administered for as long as 45 days. Pierce believes that, compared with the expense of treating and sustaining a weak foal, the $100-to-$300 investment in domperidone is nominal.

Ridding your pastures of endophyte fungus is also costly. Richard Shelby, Ph.D., of the Fescue Research Project at Auburn University in Auburn, Alabama, explains that endophyte fungus is difficult to eradicate because it is symbiotic, it actually makes the tall fescue hardier. Contaminated plants survive adverse condition that kill other, healthy plants. The only way to kill the fungus is to kill the plant. According to Shelby, elimination and control of endophyte contamination is a "massive and prohibitively expensive project" which may or may not solve the problem of toxicity. Contaminated tall fescue must be completely destroyed with a combination of herbicides and fungicides, and the pastures must then be reseeded with a mixture of endophyte-free fescue and other endophyte-resistant grasses. However, the fungus is transferred by contaminated seeds, so all efforts to maintain an endophyte-free pasture may be lost simply by a farmer spreading a contaminated bale of hay for his pasture horses. Similarly, livestock fed hay containing contaminated seeds will pass the seeds through their manure and reinfect the pastures. Birds can also spread contaminated seeds through their droppings.

Shelby's research has shown that endophyte fungus is unlike other fungi in that it cannot be detected on the plant by the appearance of spots or other abnormalities. Rather, it is contained within the living plant itself. The only way to determine if endophyte contamination exists is to have the live plants tested-a relatively inexpensive way to begin protecting your mares from this unpleasant and costly illness.