Question: We found an opossum asleep in our barn and it looks like it defecated on a stack of small square bales we feed to our horses. We are very concerned about equine protozoal myeloencephalitis (EPM), but have a limited supply of hay. Should we throw away all of our hay or is it safe to feed once we remove the feces? Do all opossums carry the microbe that causes EPM? Does the extremely cold weather we've recently had kill the microbe?
Dr. Anna Firshman, of the University of Minnesota, responds:
Equine protozoal myeloencephalitis (EPM) is a neurological disease of horses caused by the parasite Sarcocystis neurona. It can spread to horses via ingestion of hay, feed, or water that is contaminated with opossum feces.
EPM is a rare disease. Not every horse that eats contaminated feed develops EPM. Additionally, not every opossum is infected with the parasite. Studies suggest that about one third of opossums are infected in Missouri and one tenth of opossums are infected in Michigan.
While the disease is rare, it is very serious in horses. Some horses may not survive the infection even with treatment. Therefore, we do not recommend feeding horses any hay or feed that is contaminated with opossum feces. Work in other sarcocystis species suggests that the organism may survive some time in the external environment, even in freezing temperatures. Unfortunately, it is best to remove any contaminated hay from your barn and do not feed it to your horses.
Remember that opossums are important members of our wildlife ecosystem. For example, they eat large numbers of ticks, which can also cause disease in horses. Precautions to prevent EPM disease include ensuring that feed is kept in enclosed containers to prevent access by opossums. You can also take other measures within and around your barn to make it less inviting for opossums to make it their home.
- Keep things tidy. Clutter invites rodents and makes it harder to spot a potential problem.
- Regularly check your facility, especially all feed, bedding, and equipment storage rooms, for signs of wildlife presence: denning, feces, evidence of chewed material, etc.
- Secure all feed, pet food, and garbage in animal-proof containers. Feed barn cats and dogs away from where you store feed or feed horses.
- Plug any holes larger than a quarter inch to keep rodents out of barns and hay storage. Steel wool is a useful temporary plug.
- Maintain yard work around your property. Trim and clear weeds and grass close to buildings. Cut back overhanging limbs, shrubs and vines. Keep gutters clean and clear of debris.
- Inspect the farm for likely wildlife homes. Deadwood piles, old equipment, and weed and brush growth are ideal habitats for many wild animals. Animals can den or hide in areas of dense growth. Stack firewood off the ground (in racks, on pallets, etc.) and frequently inspect for signs of denning. It's best to have wood piles away from house or barn areas.
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