Equine Health Library

Performance Horse

Health Concerns

Neurologic | Gastrointestinal | Respiratory

When it comes to neurologic issues, the earlier a diagnosis can be made and treatment can begin, the better the chances are for a full recovery.

Equine Protozoal Myelopathy (EPM)

Most cases of Equine Protozoal Myelopathy (EPM) are caused by Sarcocystis neurona, which starts in the opossum and ends in the horse through contaminated hay or forage. In the U.S., the incidence of EPM has remained relatively steady at about one percent of the general horse population. The geographic range matches that of the opossum, though contaminated hay could ship and expose horses beyond the opossum’s natural domain.

Although the veterinary community is constantly working toward a proven way to prevent EPM, for now, the best way to keep your horse from getting the disease is to avoid exposing him to opossum feces.

EPM Risk Factors

  • Age, with mature horses more commonly affected than very young horses
  • Career or lifestyle, with a higher incidence among horses used for racing or western performance
  • Recent stress event such as long-distance transportation or illness
  • Season, with increased numbers of cases identified during late summer and fall
  • Management practices that include not protecting horse feeds from opossums and/or leaving pet food in the barn, which attracts opossums
  • Barns and pastures in close proximity to wooded terrain
  • History of other cases of EPM on the farm


Clinical signs vary quite a bit and include:

  • Ataxia (unsteady gait)
  • Weakness
  • Muscle atrophy (typically asymmetrical)
  • Cranial nerve deficits (including inability to swallow)
  • Decreased tongue tone
  • Ear or eyelid droop
  • Head tilt
  • Blindness
  • Seizures (rarely)

Diagnosis and Treatment

Many diseases can cause signs similar to EPM – among them, WNV, rabies, tetanus, EEE and others – but will not respond to EPM treatment. If a horse is treated for EPM, but actually has another disease, you may make a substantial investment without a positive result. Pursuing the true cause of the horse’s problem with an accurate diagnosis is considered the best practice.

In addition to a complete neurologic exam, your veterinarian will diagnose EPM with cervical radiographs to rule out Wobbler syndrome and a spinal tap and blood test to look for Sarcocystis neurona-specific antibodies.

Early detection of EPM is critical to optimize your horse’s chances for complete recovery. Approximately 30 percent of affected horses will make a complete recovery, yet most are able to successfully return to their former riding discipline.

Therapy involves daily administration of an anti-protozoal drug, such as PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets.

Important Safety Information

PROTAZIL® is contraindicated in horses with known hypersensitivity to diclazuril. The safety of PROTAZIL® in horses used for breeding purposes, during pregnancy, or in lactating mares, and use with concomitant therapies in horses has not been evaluated. Do not use in horses intended for human consumption. Not for human use. For complete safety information, refer to the product label.

Equine Herpesvirus Myeloencephalopathy (EHM)

EHM, the neurologic form of Equine Herpesvirus Type 1, is characterized by a sudden onset of ataxia (unsteady gait), loss of bladder control (e.g., dribbling urine) and reduced tail tone. EHM usually affects adult horses and is rarely reported in foals and weanlings.

EHV-1 neurologic disease may affect a single horse or up to 30 to 40 percent of horses exposed. Affected horses typically DO NOT show outward signs of respiratory disease associated with EHV-1 but do exhibit fever and depression in addition to neurologic deficits. The horse’s chance of survival diminishes once he goes down and can’t get up.

Currently, there is no vaccine labeled to prevent the neurologic form of EHV-1. Vaccination protocols decrease the severity of respiratory disease and reduce nasal shedding and circulating virus in the blood in infected horses, thereby increasing herd immunity.

Cervical facet disease

Cervical facet disease is another neurologic disease that can impact performance horses. Horses can develop arthritis in a variety of joints, including the joints between the cervical vertebrae in the neck. Degenerative arthritis involving the cervical vertebral facets can cause a variety of signs, including neck pain and stiffness as well as spinal cord and peripheral nerve root compression, resulting in incoordination or ataxia. 

Your veterinarian can detect lesions with digital radiography and ultrasound.


Because of this one-way system, problems in the gastrointestinal system can quickly become life-threatening. If your horse is uncomfortable and biting at its flanks, don’t hesitate to call your veterinarian for a diagnosis and prompt treatment.


If your show horse just doesn’t seem happy or to be performing their best, ulcers may be to blame. Gastric ulcers are erosions in the lining of the stomach. Horses in hard work or strenuous training are at the greatest risk. In fact, up to 90 percent of racehorses may be affected. Clinical signs include poor performance, weight loss, unthrifty appearance, mild diarrhea and colic. In foals, teeth grinding, and excess salivation are common signs.

Risk Factors

  • Feeding large amounts of grain at once, intermittent feeding instead of free-choice hay/grazing, and feed deprivation
  • Stress associated with heavy exercise or disease
  • Certain medications, including corticosteroids (e.g., dexamethasone) and non-steroid anti-inflammatory medications (e.g., phenylbutazone)
  • Reflux of bile acids from the small intestines back into the stomach


  • Diet changes — Include turn out onto green grass pastures or offer frequent or free-choice leafy hay meals. At least 70 percent of dry matter intake should be in the form of pasture and/or hay. If concentrates are fed, they should be fed in smaller amounts at more frequent intervals. Avoid feeding more than two to three pounds of concentrates at a single meal
  • Medications — Drugs used to reduce stomach acidity include antacids, histamine receptor antagonists (cimetidine, ranitidine) and proton pump inhibitors (omeprazole). Sucralfate is another type of medication that forms a protective barrier over ulcers and erosions to prevent further damage
  • Stress reduction — Reducing stress in the life of the equine athlete may be the most difficult therapy since stall confinement, strenuous training and long-distance or frequent transportation are often unavoidable aspects of this lifestyle


Performance horses are particularly prone to dehydration and electrolyte balances due to their active lifestyles, which can increase their risk for colic.

Because colic is a syndrome and not a disease, the term has become a catchall for any type of abdominal pain. It is literally the bellyache that can kill and is one of the leading causes of death in the horse. Fortunately, most colic cases are mild and respond well to medical therapy.

Causes and Symptoms

Abdominal pain associated with colic can be caused by a problem in the gastrointestinal tract or by a problem in another internal organ, such as colic from liver disease, heart dysfunction, bladder or kidney disease, or disorders involving the reproductive organs.

Common Gastrointestinal Causes of Colic

  • Idiopathic colic (colic of unknown cause)
  • Ileus (lack of gut motility)
  • Obstruction (due to foreign body)
  • Impaction (obstruction due to fecal material or parasites)
  • Displacements or torsions (twists) of the small or large intestines
  • Gas/spasmodic colic
  • Parasites (especially roundworms in foals and encysted larvae in adults)
  • Infarctions (obstruction of blood supply)
  • Ulcers in the stomach or intestines


Some upper airway disorders can result in decreased exercise performance as well as respiratory noise during exertion. Examples of these conditions include left laryngeal hemiplegia, aryepiglottic fold entrapment and displacement of the soft palate. Your veterinarian can diagnose many of these conditions with endoscopy at rest and during exercise.

Equine Influenza Virus (EIV)

Equine Influenza Virus (EIV) is the most frequently diagnosed cause of viral respiratory disease in adult horses. The 2007 outbreak in Australia showed the world just how devastating influenza can be to the equine industry. Prior to 2007, Australia was considered equine influenza-free.

None of the horse’s native to Australia were vaccinated against influenza, and disease prevention relied on quarantine, where all incoming horses were monitored and screened for a number of contagious diseases including influenza. A horse shedding EIV managed to leave quarantine undetected, and within nine weeks, more than 40,000 horses in nearby regions of Australia had contracted influenza.

EIV outbreaks have occurred elsewhere in the world including Europe, Japan, Mongolia, South Africa and, on a smaller scale, here in the United States. Younger horses less than 5 years of age were traditionally considered the most susceptible, however, data supports that any horse that is not properly vaccinated is at risk to develop influenza if exposed. Influenza can spread quickly because the incubation period is only 24 hours to three days, and the virus can be transmitted through the air. In fact, coughing can spread nasal droplets more than 200 yards. Horses that are sick for the first time can shed the virus in nasal secretions for as long as seven to 10 days. Indirect transmission of the virus can also occur via hands, clothing and common use articles such as bits, brushes and buckets. Vaccination is the best prevention.

Clinical Signs Include

  • High fever (>103 to 105 degrees Fahrenheit)
  • Depression
  • Dry hacking cough
  • Clear nasal discharge (that becomes thick and colored if a secondary bacterial infection develops)
  • Loss of appetite with secondary weight loss
  • Muscle soreness
  • Less common signs include distal limb edema and a rare form of heart disease (cardiomyopathy). More severe signs are observed in donkeys and mules with fatalities reported

These signs typically resolve in seven to 14 days, although the cough may persist for 21 days.

Diagnosis and Treatment

The fastest way to diagnose EIV is testing using nasal swabs. Recovering horses require a minimum of three weeks of rest or at least one week of rest for every day of fever. Premature return to exercise may be associated with complications including secondary bacterial infections, reactive airway disease and exercise intolerance.


Vaccination is the best way to prevent influenza. EIV is considered an at-risk vaccination, and horses at risk for EIV include all young horses less than 4 to 5 years of age, horses in contact with large groups of horses (e.g., at shows, on trail rides, at riding clinics, etc.) and stay-at-home horses on farms where other resident horses are going to and coming from events and shows. Mature, healthy horses, in general, are less susceptible. Most horses should be vaccinated against EIV unless they live in a closed herd or isolated facility. Frequency of vaccination is determined by risk and type of vaccine.

Biosecurity is another critical step in the prevention of influenza.

Action Items

  • Isolate new arrivals for two to three weeks and observe for fever, cough or nasal discharge
  • Monitor the daily temperature of all incoming horses for at least the first three to five days following their arrival and at the first sign of any respiratory disease or loss of appetite.

Equine Herpesvirus (EHV 1 & 4)

Equine Herpesvirus (EHV 1 & 4) are alpha herpesviruses, and though the two viruses are closely related, they are genetically and antigenically distinct. Although EHV-4 is principally associated with upper respiratory disease in younger horses (those less than 1 year of age), EHV-1 can cause respiratory disease, late-term abortions, early neonatal foal deaths and/or acute onset neurologic disease.

Most horses have been infected with EHV-1 by the time they are yearlings. Stressful events, such as hauling, handling, training and large doses of steroids, can reactivate the virus. Often times, this is asymptomatic and results in “silent” shedding – the horse does not appear to be sick but can spread the virus to other horses via nasal secretions or coughing. This is why so many outbreaks happen at show grounds.

How it’s Spread

The incubation period for EHV-1 is four to six days but can be as short as 24 hours or as long as 10 days. Clinical signs are typically observed within one to three days. Shedding of the virus typically lasts seven to 10 days but can last as long as 28 days. Longer shedding periods and higher viral loads have been reported in horses experiencing the neurologic form of the disease, Equine Herpesvirus Myeloencephalopathy (EHM), due to a neurovirulent strain of EHV-1.

Clinical signs of respiratory disease vary depending on the virus strain and immune status of the horse:

  • Two fever spikes – one to two days after infection and six to seven days after infection
  • Depression
  • Loss of appetite
  • Cough (less common)
  • Clear nasal discharge (may become thick and colored if a secondary bacterial infection occurs)
  • Conjunctivitis (reddening around the eyes)
  • Mild to moderate lymph node enlargement that can persist for weeks
  • Following recovery some horses develop “poor performance syndrome” and reactive airway disease

To diagnose EHV-1 infection, your veterinarian will submit a nasal swab and blood sample for PCR testing. Prevention includes vaccination and good biosecurity protocols.


Strangles is a highly contagious disease caused by the abscess-forming, gram positive bacteria Streptococcus equi. Approximately 75 percent of recovered horses develop solid immunity for five years or longer. Asymptomatic horses (silent shedders) can harbor the bacteria in their guttural pouches for several years and represent a source of persistent infection. The bacteria itself is hardy and survives in a moist environment and organic debris such as manure for up to six to seven weeks. Direct sunlight shortens this time period considerably.

Clinical Signs

  • High fever (≥ 103 degrees Fahrenheit). Fever is usually the first sign of disease and precedes other symptoms by 24 to 48 hours
  • Thick pus-like nasal discharge. Nasal shedding of bacteria begins one to two days after the onset of fever and can persist for two to three weeks
  • Enlarged, swollen and tender lymph nodes around the head, under the jaw and around the throat latch that frequently abscess, rupture and drain. Abscesses can also develop on other places of the body, both externally and internally. (Internal abscesses are called “bastard strangles” and are much more difficult to treat)
  • Difficulty swallowing and breathing due to enlarged lymph nodes placing pressure around the back of the throat, the esophagus and the trachea
  • Loss of appetite
  • Depression
  • Occasional soft moist cough

Diagnosis and Treatment

Your veterinarian can confirm the diagnosis of strangles using nasal swabs, nasal and guttural pouch washes and/or pus aspirated from abscesses and submitted for culture and testing. A persistent infection in a horse’s guttural pouch is best visualized using an endoscope. This is a known method for identifying horses that are silent carriers of the disease.

Once external abscesses “mature,” they can be opened, drained and flushed. Some abscesses will rupture spontaneously. Anti-inflammatory drugs such as Banamine® (flunixin meglumine paste) may be administered as needed to keep horses comfortable enough to continue eating and drinking. Discuss all medications with your veterinarian. External abscesses often require many weeks to completely resolve, and while they do, the draining pus is highly contagious. Anyone handling affected horses should wear disposable gloves and should not handle uninfected horses without first changing their clothes and washing their hands.

Internal abscesses (or “bastard strangles”) can develop in internal lymph nodes as well as in other organs. Some common internal locations include: The lungs, liver, spleen, kidney, brain and the lymph nodes lining the intestinal tract. Internal abscesses require prolonged, systemic antibiotic therapy lasting several months, and even then abscesses may not fully resolve.

Purpura hemorrhagica is an uncommon, but dreaded, complication that can occur in horses recovering from natural infection with Streptococci equi and occasionally in horses following vaccination against strangles. Purpura is an immune-mediated inflammation of the lining of blood vessels. Affected horses develop severe, pitting edema along all dependent areas of the body: Under the jaw, along the ventral abdomen and in all the limbs. Often the skin covering the edematous areas begins to ooze serum. Skin may even slough over affected regions. Purpura hemorrhagica can be life-threatening and requires aggressive treatment with antibiotics, steroids and anti-inflammatory drugs in addition to good nursing care.

Strangles Prevention

Prevention and containment of the disease should focus on hygiene, disinfection and identification of silent shedders. Horses can acquire strangles through both horse-to-horse contact and indirect transmission via contaminated shared equipment (stalls, water buckets and troughs, feeding tubs, twitches, clothing, handlers’ hands, etc.). A good biosecurity program is vital to reducing the risk of a strangles outbreak. Quarantine new arrivals for 21 to 28 days. Your veterinarian will likely recommend screening suspects or recovering horses with weekly nasal or guttural pouch washes and keep affected horses isolated until three negative cultures and PCR tests are obtained.

Your veterinarian can help design a practical biosecurity program for your operation to decrease the likelihood that your horses will contract this disease in the future.  Remember, outwardly normal horses that have recovered from an episode of strangles can be the silent shedders that begin the next outbreak. Work with your veterinarian to identify those shedders and treat them. Quarantine all new arrivals for at least two to three weeks to help prevent the introduction of strangles and other contagious diseases. Intramuscular killed vaccines, and an intranasal modified live vaccine, are available in the U.S. Vaccination during an outbreak is generally not recommended unless it is certain that the horses to be vaccinated are not incubating the disease and do not have exceptionally high antibody titers against S. equi. Your veterinarian can screen your horse for pre-existing S. equi antibodies if this is a concern.

Important Safety Information

BANAMINE: For Oral Use in Horses Only. Not for use in horses intended for human consumption.  Do not use in horses showing hypersensitivity to flunixin meglumine. The effect of BANAMINE Paste on pregnancy has not been determined. Concomitant use of Banamine with other anti-inflammatory drugs such as NSAIDs and corticosteroids should be avoided or closely monitored.  For complete information on Banamine® Paste, see accompanying product package insert.

Bacterial pleuropneumonia

Horses that travel long distances are at increased risk for severe bacterial infection of the lungs and lining of the chest cavity (the pleura). Pneumonia describes bacterial infection of the lungs. Pleuritis, an extremely painful condition, describes infection/inflammation of the lining of the chest cavity. Pleuritis causes increased production and accumulation of pleural fluid in the space between the lungs and chest wall. When these two conditions occur together, it is called “pleuropneumonia”.

Pleuropneumonia infection is usually caused by more than one type of bacteria, though the gram positive bacteria Streptococcus zooepidemicus is often one of the culprits. Other common pathogens include gram negative bacteria such as Klebsiella, Escherichia coli, Actinobacillus and Pasteurella. Many cases also involve at least one anaerobic (can live without oxygen) bacteria.

Although pleuropneumonia is rare in foals and weanlings, any breed can be affected.

Risk Factors

  • Stress
  • Transportation
  • Preceding viral infection that suppresses the immune system
  • Steroid therapy that suppresses the immune system
  • Previous episode of choke resulting in aspiration of food material

Clinical Signs

  • High fever
  • Depression
  • Rapid and shallow breathing due to the accumulation of fluid around the lungs
  • Weight loss
  • Reluctance to move due to severe chest pain
  • Nasal discharge
  • Soft cough
  • Development of pitting edema along the ventral midline originating between the forelimbs and extending back toward the hind legs

Pleuritis is very painful, and, as a result, affected horses are reluctant to move, lose their appetites and begin to take rapid, shallow breaths instead of deep breaths. Pressure applied between the ribs elicits a painful response. These signs can develop within the first 24 to 48 hours following a long trailer ride.

Listening to the lungs with a stethoscope often reveals very muffled lung sounds due to the accumulation of fluid between the outer chest wall and the surface of the lungs. Sometimes creaking rubs can be heard with each breath due to the development of adhesions on the surface of the lungs and lining of the chest wall. This is a life-threatening infection and the longer the condition goes undiagnosed, the less likely a horse is to recover completely.

Diagnosis and Treatment

Your veterinarian will diagnose pleuropneumonia based on physical examination along with ultrasound and radiography. These diagnostic tools help your veterinarian visualize the fluid accumulating in the chest cavity and identify areas of diseased and consolidated lung tissue. Cultures of the pleural fluid and of fluid from the trachea and lower airways using a transtracheal wash are usually submitted to try and identify the bacteria responsible for the infection. Blood work typically reveals an elevated white blood cell count.


  • Placement of chest tubes through the horse’s chest wall into the pleural cavity to drain off large accumulations of infected pleural fluid
  • Administration of analgesics (pain killers) to improve comfort and help keep the horse eating and drinking
  • Antibiotics for a prolonged period of time (usually weeks to months)
  • Good nutritional support
  • Intravenous fluid therapy if needed
  • Prophylactic treatment to reduce the risk of laminitis
  • Prolonged period of rest, often at least three to six months

Tips for Prevention

  • Keep horses current on vaccinations to reduce the risk of viral respiratory infections that can predispose to the development of bacterial pleuropneumonia
  • When shipping long distances, have horses in box stalls rather than cross-tied in standing stalls. Tying horses’ heads forces them to eat hay with their heads elevated, which may predispose them to aspirate feed material and associated bacteria into their lungs. This, in turn, may increase their risk for developing pleuritis and pneumonia. If horses must be shipped long distances, consider breaking up the trip with an overnight stay in a stall so the horse can move around and eat and drink in a more natural environment
  • Monitor your horse’s temperature, breathing rate and pattern, appetite and general demeanor closely for several days following any long-distance trip. Never hesitate to contact your veterinarian if something concerns you

Exercise-Induced Pulmonary Hemorrhage (EIPH)

Exercise-Induced Pulmonary Hemorrhage can be found in horses performing strenuous exercise, including flat racing, western performance and polo. Depending on the diagnostic testing used, the prevalence of EIPH varies between 40 to 85 percent of all equine athletes.

Clinical Signs

EIPH starts with bleeding in the back portion of the lungs. Severe cases exhibit a nosebleed during or immediately following exercise, but most often, the hemorrhage remains in the airways and is only visible using an endoscope.


It is believed that EIPH is caused by the rupture of small capillaries within the lungs as a result of pressure differences between the small air sacs (alveoli) and the small blood vessels during rigorous exercise. The diuretic furosemide (SALIX® (furosemide injection)) remains the most widely studied and popular drug to treat and prevent EIPH.

Important Safety Information

SALIX® (furosemide injection) is a highly effective diuretic-saluretic which if given in excessive amounts may result in dehydration and electrolyte imbalance, enhancing the risk of circulatory collapse, thrombosis, and embolism. The animal should be observed for early signs of fluid depletion with electrolyte imbalance, and corrective measures should be administered. See package insert for full information regarding contraindications, warnings, and precautions. SALIX may lower serum calcium levels and cause tetany in rare cases of animals having an existing hypocalcemic tendency. Milk taken from dairy cattle during treatment and for 48 hours (four milkings) after the last treatment must not be used for food. Cattle must not be slaughtered for food within 48 hours following last treatment. Do not use in horses intended for human consumption.

Equine Asthma Syndrome

Recently, the American College of Veterinary Internal Medicine (ACVIM) updated and reclassified its recommendations to better describe a variety of chronic airway inflammatory disorders in horses, including inflammatory airway disease (IAD) and recurrent obstructive airway disease (RAO), as “equine asthma syndrome.”

Inflammatory Airway Disease (IAD)

Also referred to as small airway disease, inflammatory airway disease is observed in young to middle-aged athletes with the primary symptoms of poor performance, exercise intolerance, coughing and excess mucus production. Affected horses usually do not have a fever unless a secondary infection develops.


The cause of IAD varies and can be low-grade viral infection, inhaled molds and organic dusts (mites, endotoxin), exposure to air-borne pollutants, inhaled cold air during exercise and/or pulmonary hemorrhage. Diagnosis may include special pulmonary function tests during exercise, bronchoalveolar lavage and thoracic ultrasound.


Therapy focuses on reducing and controlling airway inflammation using inhaled and systemic steroids and other drugs designed to reduce airway responsiveness. Environmental changes are aimed at reducing exposure to inhaled irritants and pollutants, feeding wet hay, replacing straw bedding with shavings and keeping horses outside as much as possible.

Recurrent Obstructive Airway Disease (RAO)

Often referred to as heaves, RAO is actually a hypersensitivity reaction to inhaled organic dusts, such as mites and endotoxin and/or molds found in poorly cured hay. You’ll see this condition more often in stalled horses and in the northeastern and mid-western states.

In the southern United States, a similar disorder called summer pasture associated obstructive pulmonary disease (SPAOPD) occurs in horses grazing pastures during summer and fall months. Inhaled fungal spores and grass pollens are the environmental triggers. Many refer to RAO as the equine version of human asthma.

Signs of RAO or SPAOPD

  • A cough, often exercise-induced.
  • Nasal discharge consisting of mucus and pus.
  • Exaggerated expiratory effort (forced breathing).
  • Increased respiratory rates even at rest.
  • Chronic cases may have a “heave line” due to enlargement of the respiratory muscles associated with the increased work of breathing.
  • Listening to the chest often reveals abnormal lung sounds including wheezes and crackles.

For more information on Recurrent Obstructive Airway Disease, click here to read more on the AAEP.