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Possum poop may be problematic to horses

When evaluating the quality of horse hay, it is important to consider the moisture, protein, digestible energy and nutrient content. You may be looking to hold the nonstructural carbohydrate level below 10% for horses with metabolic syndrome, or maybe you need to limit the dustiness for horses with respiratory issues.

But if you’ve seen evidence that opossums may have gotten into your horse’s hay supply, you may have even more urgent worries.

Opossums (or just “possums” for us Midwest country folks) are hosts for equine protozoal myeloencephalitis (EPM), a disease that affects the brain and spinal cord. EPM is considered rare but serious. Infected horses may not survive, even with treatment.

DrJimWhiteThe neurologic disease can spread to horses consuming forage, feed or water contaminated with possum feces containing the EPM-causing organism, Sarcocystis neurona. Possums are not picky and will eat about anything they can find. They also defecate indiscriminately, unlike raccoons or hogs that have a distinct latrine area.

Once a horse ingests Sarcocystis neurona, the organism can enter gastrointestinal tract, then the bloodstream and then the central nervous system. Horses are “dead end” hosts, so once infected, they cannot transmit it to other animals.

Not every horse that eats contaminated feed develops EPM, and not every possum carries the parasite that causes EPM. Wildlife biologists report that about a third of Missouri possums are infected. Reports indicate that 50% to 60% of horses have been exposed to Sarcocystis neurona, but only about 1 out of 600 develop the disease.

Dr. Tony Martin, MFA’s manager of animal health, says the sooner EPM is diagnosed and appropriately treated, the better the chance of recovery without permanent damage. That means examining affected horses in early symptomatic stages and including EPM in the initial differential diagnosis list if any of the clinical signs give even a hint of the disease. Tests of both blood and spinal fluid are the gold standard for identifying EPM.

To help remember symptoms of EPM, just think “STALL.”
• Stumbling or tripping
• Tilted head with poor balance
• Asymmetric muscle weakness
• Lameness or gait abnormality
• Leaning against walls

Affected horses may also have difficulty swallowing, suffer from seizures, sweat abnormally, and exhibit drooping eyes, ears or lips.
Marquis, an antiprotozoal medication with the active ingredient ponazuril, is the primary treatment of choice for EPM, along with anti-inflammatory medications to lessen neural swelling and damage. Many severely affected horses can be treated and survive, but quality of life and function tend to lead to euthanasia in extreme cases.

There is also at least a 10% to 20% chance of relapse in horses that are successfully treated.

Currently, no vaccination is available for EPM, so prevention relies on maximizing your horse’s health and reducing the chances that possum feces is present in feed, hay or water. Start by taking measures to deter possums from entering barns, hay sheds and outbuildings. Possums prefer to be left alone. They want to eat, sleep, have more possums, stay unnoticed by larger animals and not get run over by cars.

Monitor barns, feed storage areas and stall bedding for signs of pest presence, such as gnawed bags and animal nests. Woodpiles and abandoned equipment are also favorite denning sites for a number of pests, not just possums but also skunks, armadillos and other disease-spreading wildlife that could carry the EPM organism.

Feed pets away from the barn—or at least away from where you are storing feed and hay. Bird feeders and fallen fruit are also attractive to wildlife such as possums.

Keep building perimeters free from grass and weeds that could provide cover for rodents. Cut back any overhanging trees or vines. Reducing places they can hide and keeping feed in rodent-proof containers will also preclude possums.

Hopefully, the only part of this article you’ll ever need are the tips on “prevention,” but if you have questions, reach out to the experts at your local MFA or email This email address is being protected from spambots. You need JavaScript enabled to view it..

CLICK HERE to read more from this November Today's Farmer Magazine.

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