EPM is a challenging disease in horses due to its challenging symptoms and diagnosis.
If your horse has been diagnosed with EPM or you're beginning to notice EPM symptoms, there are proactive steps you can take to slow the progression and support their recovery.
This guide will help you better understand EPM, recognize its symptoms, understand the diagnosis, and explore EPM treatment options for horses, ranging from natural and nutritional approaches to medical therapies.
What is EPM in Horses?
Equine Protozoal Myeloencephalitis (EPM) is an infectious disease that targets a horse’s central nervous system and is caused by protozoan parasites.
EPM was first identified in 1964 by a veterinarian in Kentucky, and by the 1970s, scientists had linked the disease to protozoal infection. Since then, ongoing research has aimed to deepen our understanding of this often-debilitating neurological condition.
The prevalence and severity of Equine Protozoal Myeloencephalitis (EPM) can vary greatly depending on where you live. While exposure to the protozoa that cause EPM is common, only a small number of horses develop clinical signs of the disease. Studies show that EPM cases are typically isolated, rarely affecting more than one horse on a given property.
The primary culprit is Sarcocystis neurona, though a less common cause is Neospora hughesi. Horses typically become infected with Sarcocystis neurona by ingesting feed, hay, or water contaminated with feces from opossums carrying the parasite. In contrast, the definitive host for Neospora hughesi has yet to be identified.
While transplacental transmission of Neospora hughesi, resulting in infected foals, has been reported, this mode of transmission has not been observed with Sarcocystis neurona.
What Horses Are at Higher Risk of Developing EPM?
It’s estimated that up to 50% of horses have been exposed to the sporocysts responsible for causing EPM. Although many horses are exposed to the sporocysts that cause EPM, only a small percentage develop the disease. One study found that just 14 in 10,000 horses show symptoms.
Immune function plays a key role, with horses with weakened immune systems being more susceptible. Stressful events, such as heavy exercise, transport, injury, surgery, or parturition, can also increase the risk by suppressing the immune system. Race and show horses are at a higher risk due to the additional stressors they face.
Horses living in certain regions, particularly the eastern United States, are also at a higher risk of developing EPM. The majority of EPM cases are reported in the following states:
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Kentucky
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Michigan
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Missouri
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New Jersey
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New York
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Ohio
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Pennsylvania
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Tennessee
These regions pose a greater risk due to larger opossum populations and environmental conditions that facilitate the protozoa's survival more easily.
Risk factors also include age and sex, with younger horses and males being more susceptible. Males, especially stallions, are approximately twice as likely to develop EPM as female horses. Breed may also play a role, as studies have shown a higher incidence of EPM in Standardbreds, Tennessee Walking Horses, Thoroughbreds, and Warmbloods. Conversely, Quarter Horses, ponies, drafts, and other breeds appear to have a lower rate of infection.
Symptoms of EPM in Horses
Horses affected by EPM often appear bright, alert, and responsive in the early stages of the disease.
The disease primarily affects the spinal cord but can impact almost any part of the central nervous system, leading to a wide range of neurological symptoms. Symptoms may begin gradually or appear suddenly. Some horses experience steady worsening, while others may stabilize temporarily before relapsing days or weeks later. Severity of EPM can range from mild to severe, often worsening if left untreated.
Common symptoms of EPM in horses include:
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Weight loss
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Asymmetrical or symmetrical ataxia (lack of coordination), often worse on one side
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Muscle atrophy, particularly over the topline, hindquarters, rump, or shoulders
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Generalized weakness or hind-end weakness
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Lameness that comes and goes or shifts sides
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Stiff or stilted gaits
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Abnormal posture or leaning against stall walls for support
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Difficulty balancing, especially when a hoof is lifted
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Circling, slipping, or stumbling during movement
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Dragging a hoof, especially while turning
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Sore or sensitive back
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Unusual sweating patterns
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Tail carried off to one side or held away from the body
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Lethargy or decreased energy levels
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Drooping lip
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Facial twitching
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Facial paralysis
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Drooping ear
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Difficulty chewing or dropping feed
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Trouble swallowing
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Head tilt
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Abnormal eye movements (nystagmus)
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Seizures or sudden collapse (in rare or advanced cases)
Because EPM can be life-threatening, it should always be taken seriously. If you suspect your horse may be showing signs of the disease, prompt veterinary evaluation is essential.
Diagnosing EPM in Horses
Despite years of extensive research, many aspects of EPM remain unclear. Because the protozoa can impact any part of the central nervous system, virtually any neurological symptom is possible.
Diagnosing EPM can be difficult, as its symptoms often mimic those of other neurological disorders. A definitive diagnosis can only be made through postmortem detection of the protozoa.
However, veterinarians can often form a presumptive diagnosis based on clinical signs that align with EPM. A thorough neurological exam is typically the first step in the diagnostic process. To narrow down the cause, they may rule out other neurological conditions with similar symptoms, such as Wobbler syndrome, Lyme disease, rabies, or Cushing's disease.
A veterinarian may form a suspected diagnosis of EPM based on the following criteria:
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The presence of neurological signs consistent with EPM
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Ruling out other neurological disorders
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Detection of specific antibodies to either S. neurona or N. hughesi in serum and cerebrospinal fluid (CSF)
Treatment Options for EPM in Horses
Fortunately, several FDA-approved treatments are available and are most effective when started early in the progression of the disease.
EPM is typically treated with anti-protozoal medications, often in combination with supportive care, including rehabilitation, nutritional support, and inflammation control. The three FDA-approved treatments for EPM are Ponazuril (Marquis), Diclazuril (Protazil), and Sulfadiazine and Pyrimethamine (Re-Balance).
· Ponazuril, given once daily for 28 days
· Diclazuril, a pelleted, alfalfa-based top-dressing fed daily for 28 days
· Sulfadiazine and pyrimethamine, an oral suspension given once daily for up to 120 days
These medications function by preventing protozoa from reproducing and targeting the specific protozoa that cause EPM for elimination. The goal is to reduce the protozoa load to a level where the horse’s immune system can take over and resolve the disease. Consequently, supporting the immune system is crucial in treating EPM.
Anti-inflammatory medications can also be beneficial in treating EPM. Flunixin meglumine (Banamine) is often administered to horses with moderate to severe symptoms during the first 3-7 days of treatment. For horses showing severe symptoms, corticosteroid therapy may also be recommended.
Your veterinarian will tailor the specific treatment plan based on your horse’s symptoms and the severity of the disease. Relapse of EPM within 1-3 years after treatment occurs in approximately 10% of horses affected by the disease.
Treating EPM Naturally and Nutritionally
In addition to the prescribed medical treatment for EPM, there are nutritional strategies you can implement to support your horse's recovery and help treat EPM naturally.
Vitamin E Supplementation
If your horse has been diagnosed with EPM, your veterinarian may have recommended a Vitamin E supplement. This is because natural Vitamin E is a powerful antioxidant that supports nerve function and boosts the immune system. It is generally recommended to provide 5,000 to 10,000 IU per day during EPM treatment. Vitamin E levels in your horse's blood can be monitored, and the supplement amount may be adjusted for long-term use if needed.
A nutritionally balanced diet is crucial for horses with EPM to ensure they are receiving all the necessary vitamins and minerals, as many nutrients play a role in supporting the immune system beyond Vitamin E.
Immune Support
Reducing your horse’s stress levels, such as allowing them to live with other horses, limiting hauling, and reducing intense exercise, is crucial. Supporting your horse’s immune system, both during and after EPM treatment, helps minimize the severity of symptoms and lowers the risk of relapse.
The most effective way to support your horse’s immune function is by feeding a natural diet, primarily consisting of high-quality forage (2-3% of the horse's body weight). Avoid poor-quality horse feeds as much as possible, as they can promote inflammation and contribute to metabolic issues.
You can also enhance your horse’s immune support by providing a balanced vitamin and mineral supplement that includes antioxidant support, including Vitamin E, selenium, and Vitamin C. This can be achieved by feeding a high-quality ration balancer, like Essential K® or Wholesome Blends® Balancer.
You can add 2 pounds per day of either ration balancer for an extra nutrient boost. If your horse is already on a full intake feed (4+ pounds per day), you can add an additional pound of Essential K® or Wholesome Blends® Balancer on top of their regular feed.
Muscle Support and Muscle Recovery
Since muscle atrophy is a common symptom of EPM, supporting muscle rebuilding with high-quality protein is essential. Focus on feeding adequate levels of lysine, methionine, and threonine to support muscle recovery.
Products like Essential K® Rebuild are an excellent option for providing essential vitamins, minerals, turmeric and amino acids necessary for muscle rebuilding and overall support during EPM recovery.
Weight Gain and Weight Support
Many horses with EPM experience significant weight loss and may require weight gain during recovery.
A high-fat supplement, such as K Finish®, can provide healthy calories with ingredients like full-fat soybeans, flaxseed, rice bran, and omega-3 fatty acids, which also improve coat quality.
Full-intake feeds like Synergize® that are very high in fat (13%), high in fiber (20%), and low in non-starch carbohydrates (NSC) (15%), make them suitable for horses with the highest calorie needs that also have sensitivities to sugar and starch.
Natural Anti-Inflammatory Supplementation
Since EPM is an inflammatory condition, incorporating a natural anti-inflammatory supplement, such as Natural Remedy, can be beneficial.
Natural Remedy contains DHA and omega-3 fatty acids that help reduce inflammation while also supporting immunity, heart, and respiratory functions.
Get a Customized Feed Plan for Your Horse
Feeding a horse with EPM can be complex, as nutritional needs often change from diagnosis through recovery.
Working with Tribute®’s equine nutrition experts allows you to create a customized feeding plan tailored to your horse’s unique needs at every stage. Tribute can help you design a personalized feed plan to support your horse during treatment and recovery, and maintain optimal health once treated.
