Introduction to Major Respiratory Diseases in Horses: Signs, Differentiation, Treatment, and Prevention
Respiratory disease can affect a horse at any age and range from an occasional cough to a life-threatening inability to breathe. Some conditions spread quickly through a barn. Others develop because of dust, structural problems, parasites, tumors, or strenuous exercise. A horse may even look normal at rest while struggling during work.
Because breathing directly affects stamina and recovery, coughing, unusual noise, changed nasal discharge, or unexplained loss of performance deserves attention. This article explains the major signs, diseases, and diagnostic tests so owners can observe and report problems accurately. It does not replace a veterinary examination. Breathing distress, nosebleeds, frothy discharge, or signs of contagious disease require prompt veterinary care.
This article provides an introductory overview of the major respiratory diseases that affect horses. It is designed to help owners and students recognize important signs, understand how veterinarians investigate respiratory problems, and learn the basic principles of treatment, management, and prevention. Because each condition is complex, this overview cannot cover every disease in full detail. Readers are encouraged to follow the links throughout the article for more in-depth information on individual diseases, diagnostic procedures, vaccination, biosecurity, and respiratory care.
How the Equine Respiratory System Works
Every breath carries air through the nostrils, nasal passages, pharynx, larynx, trachea, bronchi, and progressively smaller airways before it reaches the alveoli. The alveoli are tiny air sacs where oxygen moves into the blood and carbon dioxide moves out.
The upper respiratory tract includes the nostrils, nasal passages, paranasal sinuses, pharynx, larynx, and guttural pouches. Its job is to conduct, warm, humidify, and filter incoming air. The lower respiratory tract includes the trachea, bronchi, bronchioles, alveoli, lungs, and pleural space surrounding the lungs. This is where air is distributed and gas exchange occurs.
Horses are obligate nasal breathers. Under normal conditions, they breathe through their nostrils rather than switching to mouth breathing. Any narrowing of the nasal passages, pharynx, or larynx can therefore have a major effect on airflow, especially during fast work.
The horse has several built-in respiratory defenses:
The complex nasal passages create turbulent airflow that directs many inhaled particles toward mucus-covered surfaces.
Mucus traps dust, microorganisms, and debris.
Microscopic cilia lining the airways move mucus toward the throat, where it is swallowed. This process is called the mucociliary escalator.
Coughing helps clear material from the trachea and larger bronchi.
Alveolar macrophages, a type of immune cell, engulf particles and microorganisms that reach the deepest areas of the lungs.
Antibodies, antimicrobial proteins, lymphoid tissue, and the normal respiratory microbiome help limit infection.
These defenses are effective, but they can be overwhelmed or damaged. Viral infection may injure the ciliated lining of the airways. Long trailer rides with the head held high can interfere with drainage. Choke or difficulty swallowing can allow saliva, feed, or medication to enter the lungs. Dust, mold spores, endotoxins, ammonia, pollen, and smoke can drive inflammation. Stress, severe illness, anesthesia, and immune suppression can also make the lower respiratory tract more vulnerable to infection.
Did You Know? A barn can look clean and still contain high concentrations of respirable particles. The smallest particles may be invisible, yet they can travel deep into the lungs and contribute to airway inflammation.
Four Useful Ways to Classify Respiratory Disease
Respiratory problems become easier to understand when they are sorted into broad groups. A single disease can fit into more than one category.
Classification | What it means | Common examples |
Upper airway | Affects structures from the nostrils through the larynx and guttural pouches | Sinusitis, guttural pouch disease, laryngeal paralysis, soft palate displacement |
Lower airway | Affects the trachea, bronchi, lungs, alveoli, or pleural space | Equine asthma, pneumonia, pleuropneumonia, EIPH |
Infectious | Caused by a virus, bacterium, fungus, or parasite | Influenza, EHV, strangles, bacterial pneumonia, lungworm |
Noninfectious | Caused by inflammation, structural dysfunction, hemorrhage, toxins, or tumors | Equine asthma, recurrent laryngeal neuropathy, EIPH, pulmonary neoplasia |
Contagious and infectious do not mean exactly the same thing. Equine influenza and strangles are both infectious and readily contagious. Aspiration pneumonia is infectious once bacteria establish in the lungs, but it does not usually spread from that horse to others. Equine asthma is inflammatory and noncontagious. This distinction matters because isolation protects other horses only when a transmissible disease may be involved.
Signs of Respiratory Disease in Horses
Respiratory signs vary with the problem's location, cause, severity, duration, and the horse's activity level.
Common signs include:
Coughing at rest, during feeding, at the beginning of exercise, or during strenuous work
Clear, white, yellow, green, bloody, or foul-smelling nasal discharge
Fever
Increased respiratory rate at rest
Flared nostrils
Greater abdominal effort while breathing
Rapid, shallow breathing
Extended head and neck
Unusual breathing sounds, including roaring, whistling, rattling, snoring, or high-pitched stridor
Reduced appetite, depression, or lethargy
Enlarged or painful lymph nodes under the jaw or around the throat latch
Facial swelling, tearing from one eye, or reduced airflow through one nostril
Feed, water, or saliva coming from the nostrils
Poor performance, slow recovery, or an unexplained unwillingness to work
Weight loss or loss of condition
Blood from one or both nostrils
The Horse Education Online guide to cough in horses and the guide to nasal discharge in horses can help owners document these signs while arranging appropriate veterinary care.
Respiratory rate and effort
A healthy adult horse at rest commonly takes about 8 to 16 breaths per minute, although reference ranges vary slightly. Exercise, excitement, pain, weather, body condition, and fitness can affect the number. The best comparison is a reading taken when the horse is calm, cool, and healthy.
Count one rise and fall of the flank as one breath. Watch for a full minute if the pattern is irregular. Record the number and describe the effort. “Twelve breaths per minute, quiet and easy” gives a veterinarian more useful information than the number alone. The Horse First Aid and Vitals guide explains how to check respiration, temperature, pulse, gums, and other important baseline findings.
Increased effort can be more important than a mildly increased rate. Horses with upper-airway obstruction often work hardest while breathing in. They may make an inspiratory noise because narrowed or unstable tissue is being pulled toward the airway. Horses with lower-airway obstruction, especially severe equine asthma, often have a prolonged and forceful expiration. They may recruit the abdominal muscles to push air out through narrowed bronchi.
Rapid, shallow breathing can occur with restrictive lung disease, pneumonia, pleural pain, or fluid around the lungs. These horses may be unable or unwilling to take a deep breath.
What nasal discharge can tell you
Small amounts of clear, bilateral discharge may occur briefly after exercise or exposure to cold air. Persistent discharge, a change in color, a foul odor, or discharge from only one nostril requires closer attention.
Unilateral discharge often points toward a problem on one side of the head, such as dental-root disease, sinusitis, a foreign body, a mass, or a guttural pouch disorder. Bilateral discharge is more common with widespread upper-airway infection or material rising from the trachea and lungs, although exceptions occur.
The character of the discharge also matters:
Clear or watery discharge may accompany irritation, early viral disease, or allergy.
Thick white, yellow, or green discharge suggests mucus, inflammatory cells, and possibly bacterial infection.
A foul odor raises concern for sinus infection, dental disease, tissue breakdown, or anaerobic bacterial infection.
Feed or saliva from the nostrils suggests difficulty swallowing or choke and creates a risk of aspiration pneumonia.
Blood may originate from the nasal passages, sinuses, guttural pouches, a mass, trauma, or the lungs after strenuous exercise.
Never assume that blood from the nostrils is a harmless “bleeder” episode. Guttural pouch mycosis can erode a major artery and cause fatal hemorrhage. A veterinarian must determine the source.
Cough and breathing noise
A cough is protective, but repeated coughing signals irritation, mucus, inflammation, obstruction, or infection. Note when it occurs. Cough with hay may suggest dust or swallowing difficulty, while cough at the start of work is common with lower-airway mucus. A sudden cluster of coughing horses suggests infection. A weak cough in a very sick horse can be especially concerning because pain or exhaustion may limit airway clearance.
Breathing noise provides clues about location. A low-pitched roar during exercise is commonly associated with recurrent laryngeal neuropathy. A fluttering or gurgling sound during fast work may occur with dorsal displacement of the soft palate. High-pitched stridor at rest indicates serious upper-airway narrowing. Snoring and uneven airflow through the nostrils can occur with unilateral nasal obstruction. Some dynamic obstructions make no noise at rest and become apparent only during exercise.
Loss of performance may be the only sign
Mild-to-moderate equine asthma, exercise-induced pulmonary hemorrhage, and dynamic upper-airway disorders may be invisible during a routine barn examination. The horse may have no fever and breathe normally at rest, yet tire early, lose speed, recover slowly, or cough only during work.
Respiratory disease is only one cause of poor performance. Lameness, cardiovascular disease, anemia, muscle disorders, pain, conditioning, and training problems can look similar. Veterinary investigation is more useful than treating presumed “allergies” or “bleeding” based only on performance.
Did You Know? A horse can have important lower-airway inflammation while appearing completely normal at rest. Exercise history and airway sampling may reveal disease that a basic examination cannot detect.
Respiratory Red Flags: When to Call the Veterinarian Urgently
Call a veterinarian promptly when a horse has any of the following:
Labored breathing or obvious respiratory distress at rest
Marked nostril flare, an anxious expression, or the head and neck held out to breathe
Blue, purple, gray, very dark, or poorly perfused gums
High-pitched airway noise or rapidly worsening obstruction
Frothy or blood-tinged fluid from the nostrils
Moderate or heavy bleeding from one or both nostrils
Feed, water, or saliva coming from the nose
Fever combined with cough, nasal discharge, depression, or swollen lymph nodes
A respiratory rate that remains well above the horse's normal baseline after rest and cooling
Chest pain, reluctance to move, or standing with the elbows held away from the body
Sudden deterioration after a long trailer ride, choke, anesthesia, or respiratory infection
Collapse, weakness, incoordination, or difficulty urinating accompanying fever or respiratory signs
Similar signs appearing in more than one horse
If contagious disease is possible, stop horse movement, separate the affected horse, avoid shared buckets and equipment, and call the veterinarian before moving through the rest of the barn. The Infectious Disease Isolation Assistant provides a practical starting point, but the attending veterinarian and animal-health authorities should direct an outbreak response.
What Information the Veterinarian Needs
A good history can narrow the list of possible causes before testing begins. Record:
The horse's age, breed, use, and current workload
When the problem began and whether it is improving, stable, or worsening
Temperature, pulse, respiratory rate, and breathing effort
The frequency and timing of cough
The color, odor, amount, and one-sided or two-sided nature of nasal discharge
Any respiratory noise and whether it occurs at rest or during exercise
Recent travel, shows, sales, new arrivals, or contact with outside horses
Vaccination history and dates
Housing, ventilation, bedding, hay type, round-bale access, and visible dust or mold
Recent choke, difficulty swallowing, dental problems, anesthesia, surgery, or medication administration by tube
Exposure to smoke, wildfire ash, agricultural chemicals, or unusual plants
Deworming history and contact with donkeys or mules
Previous treatments and the horse's response
A written timeline is more reliable than memory. The Horse Health Log or Horse Tracker can keep temperatures, symptoms, medications, travel, vaccines, and veterinary notes together.
How Veterinarians Examine and Diagnose Respiratory Disease
The veterinarian begins by watching the horse breathe without unnecessary handling. Respiratory rate, depth, rhythm, nostril flare, abdominal effort, posture, airflow through each nostril, and audible noise all provide clues. The head, throatlatch, lymph nodes, trachea, and chest are then examined. The veterinarian listens for normal airflow and abnormal sounds such as wheezes, crackles, reduced breath sounds, or pleural friction rubs.
No single test identifies every respiratory disease. Test selection depends on whether the suspected problem is in the upper airway, lower airway, pleural space, or several areas at once.
Endoscopy
An endoscope is a flexible camera passed through a nostril. It allows direct examination of the nasal passages, pharynx, larynx, guttural pouch openings, trachea, and visible larger airways. Endoscopy can reveal mucus, pus, blood, masses, inflammation, structural abnormalities, laryngeal dysfunction, guttural pouch disease, and the source of some forms of discharge.
Standing endoscopy is useful for many conditions, but it cannot reproduce every problem that occurs during work. Dynamic endoscopy records the upper airway while the horse exercises on a treadmill or performs its usual discipline under saddle. It is especially valuable for intermittent soft palate displacement, dynamic pharyngeal collapse, and some grades of laryngeal dysfunction.
Ultrasound and radiographs
Thoracic ultrasound evaluates the surface of the lungs and pleural space. It is particularly useful for locating pleural fluid, pulmonary consolidation close to the chest wall, abscesses, fibrin, masses, and abnormal pleural surfaces. It can also guide safe collection or drainage of fluid.
Radiographs show deeper areas that ultrasound cannot reach through air-filled lung. They may identify pneumonia patterns, abscesses, interstitial disease, fibrosis, masses, pneumothorax, or changes around the mediastinum. Skull radiographs can help identify sinus fluid, dental disease, fractures, and masses.
Computed tomography, or CT, provides cross-sectional images of the head and upper airway. It helps separate overlapping dental roots, sinuses, nasal structures, guttural pouches, or masses. MRI may be selected for certain soft-tissue or neurologic problems. Availability, horse size, cost, and sedation or anesthesia requirements affect the choice.
Nasal swabs, blood tests, culture, and PCR
Bloodwork may reveal inflammation, infection, anemia, dehydration, immune changes, or organ involvement, but it rarely identifies the cause by itself. Nasal or nasopharyngeal samples can be tested by polymerase chain reaction, or PCR, for viral or bacterial genetic material. Culture may identify living bacteria and help the veterinarian select an effective antimicrobial.
Timing and sample location matter. A negative nasal swab does not rule out every infection, especially early in disease or when the organism is hidden in the guttural pouches. Veterinarians may collect paired samples, repeat testing, or sample a more appropriate location when clinical suspicion remains high.
Transtracheal wash and bronchoalveolar lavage
A transtracheal wash collects secretions from the trachea through a sterile approach. It is commonly used when bacterial pneumonia is suspected because the sample can be examined and cultured without contamination from the nose and throat.
A bronchoalveolar lavage, or BAL, samples fluid and cells from smaller lower airways. It is often the preferred test for equine asthma and other inflammatory airway diseases. Cytology, the microscopic examination of those cells, can show increased neutrophils, mast cells, eosinophils, blood, fungal elements, or other abnormalities.
The procedures answer different questions. A transtracheal sample is useful for culture in suspected infection, while a BAL gives a better picture of deeper-airway inflammation. They are not automatic substitutes.
Pleural fluid testing and advanced procedures
When fluid accumulates around the lungs, the veterinarian may perform thoracocentesis to collect and sometimes drain it. The fluid's appearance, protein level, cell population, odor, cytology, and culture can help distinguish infection, bleeding, cancer, and other causes.
Pulmonary function testing is available at some referral centers and can measure airway resistance, lung compliance, airflow, and airway responsiveness. Lung biopsy or thoracoscopy may be required when interstitial disease, fibrosis, fungal pneumonia, or cancer cannot be confirmed in a safer way. These procedures are reserved for carefully selected cases because they carry risks, including bleeding and pneumothorax.
Did You Know? A transtracheal wash and a BAL are not interchangeable tests. One is often chosen to identify infection and culture bacteria, while the other is used to characterize inflammation in the smaller airways.
Upper Respiratory Tract Disorders
Upper-airway disease can interfere with breathing, swallowing, drainage from the sinuses, and athletic airflow. Some conditions are obvious at rest. Others appear only when air demand rises during exercise.
Rhinitis, sinusitis, and dental-related sinus disease
Rhinitis is inflammation of the nasal passages. Sinusitis is inflammation or infection within one or more paranasal sinuses. Viral infections can affect both sides, while bacterial, fungal, dental, traumatic, and mass-related problems are more likely to cause persistent one-sided disease.
The upper cheek teeth sit close to the maxillary sinuses, so root infection can spread into a sinus. Owners may see thick unilateral discharge, strong odor, facial swelling, tearing from one eye, reduced airflow, or facial discomfort. Antibiotics may help temporarily, but they cannot correct a diseased tooth, remove a mass, or empty thick material from a sinus.
Diagnosis may involve oral and dental examination, endoscopy, skull radiographs, sinuscopy, or CT. Treatment is directed at the cause and may include removing an affected tooth, flushing or surgically draining the sinus, debriding abnormal tissue, and using targeted antimicrobial or antifungal medication. Recurrence is more likely when a mass, extensive dental disease, or progressive ethmoidal hematoma is present.
Progressive ethmoidal hematoma is a noncancerous but expanding mass of blood and fibrous tissue, usually deep in the nasal cavity of a mature or older horse. Intermittent bloody discharge from one nostril is classic, though larger lesions can cause bilateral discharge, facial distortion, cough, bad breath, or breathing difficulty. Endoscopy and imaging establish its extent. Treatment may involve medication injected into the mass, laser treatment, or surgery. Recurrence is common.
Guttural pouch disorders
The guttural pouches are paired air-filled extensions of the auditory tubes located behind the throat. Major arteries and several cranial nerves run along their walls. This close relationship explains why disease in a guttural pouch can cause bleeding, difficulty swallowing, voice changes, facial nerve problems, or laryngeal dysfunction.
Guttural pouch tympany occurs most often in foals. Trapped air produces a soft, generally painless swelling behind the jaw. Severe distention can interfere with breathing or swallowing and contribute to aspiration pneumonia. Endoscopy and radiographs confirm the problem. Surgical correction generally carries a favorable prognosis.
Guttural pouch empyema is an accumulation of pus, commonly following strangles. Thick material may dry into firm masses called chondroids. Affected horses may have chronic or intermittent nasal discharge, swollen lymph nodes, parotid swelling, or increased breathing noise. Endoscopy allows the veterinarian to inspect and sample the pouches. Repeated lavage may remove fluid material, while chondroids often require endoscopic or surgical removal. PCR and culture are important because an apparently healthy horse with retained infected material can continue to spread Streptococcus equi.
Guttural pouch mycosis is a fungal disease and a true emergency. A fungal plaque can damage an artery running through the pouch, resulting in repeated nosebleeds or sudden fatal hemorrhage. Nerve damage may cause difficulty swallowing, feed or water from the nostrils, an abnormal voice, facial weakness, or laryngeal paralysis. Treatment usually focuses on closing the affected artery through an interventional surgical procedure before catastrophic bleeding occurs. Antifungal treatment alone cannot be relied upon to protect an eroded vessel. A horse with unexplained or recurrent epistaxis should be kept quiet and examined urgently.
Did You Know? The guttural pouches are close to arteries that supply the head and to nerves involved in swallowing and laryngeal function. That is why one guttural pouch disorder can produce signs that seem unrelated, including nosebleeds, difficulty eating, facial changes, and airway noise.
Pharyngeal lymphoid hyperplasia
Young horses entering training commonly develop prominent lymphoid tissue along the back of the pharynx, called pharyngeal lymphoid hyperplasia. It reflects immune stimulation and may follow pathogen exposure or a new training environment. Mild cases often improve with time and reduced work. Persistent disease may contribute to cough, poor performance, or nearby airway instability. Endoscopy grades the tissue and rules out other causes.
Dynamic and structural upper-airway obstruction
During intense exercise, upper-airway tissues that look normal at rest may become unstable. Dynamic endoscopy is often the only way to see the obstruction.
Common or important disorders include:
Dorsal displacement of the soft palate: The back edge of the soft palate moves above the epiglottis and partially blocks airflow, usually during intense work. Horses may make a low, fluttering or choking noise and suddenly lose speed. Resting endoscopy can miss it. Management may include fitness and equipment changes, treatment of inflammation, or surgery, depending on the horse and the confirmed mechanism.
Recurrent laryngeal neuropathy: Commonly called roaring or laryngeal hemiplegia, this is usually progressive loss of nerve supply to the left side of the larynx. The arytenoid cartilage fails to open normally during inspiration. Tall horses and draft breeds have increased risk. Endoscopy at rest and sometimes during exercise establishes severity. Surgical options depend on the horse's job and obstruction.
Epiglottic entrapment: A fold of tissue covers the free edge of the epiglottis. The horse may make respiratory noise, cough while eating or exercising, and show reduced performance. Endoscopy confirms the condition, and surgical division of the entrapping tissue usually offers a good prognosis.
Arytenoid chondritis: Infection and inflammation damage one or both arytenoid cartilages. Granulation tissue, swelling, and reduced movement can cause serious airway narrowing and stridor. Medical care alone is not always curative, and surgery or a temporary or permanent tracheostomy may be required in advanced cases.
Rostral displacement of the palatopharyngeal arch: This uncommon developmental malformation changes the back of the throat and larynx. It can impair breathing and swallowing and lead to aspiration pneumonia. The prognosis for high-level athletic function is guarded.
Nasopharyngeal cicatrix syndrome: Inflammation followed by scar formation narrows the pharynx and may involve the epiglottis, larynx, and guttural pouch openings. It is reported mainly in the Gulf Coast region, particularly parts of Texas, and may be associated with pasture exposure during warm months. Early removal from the suspected environment may slow progression. Severe obstruction may require a permanent tracheostomy.
Congenital abnormalities: Choanal atresia, cleft palate, subepiglottic cysts, and underdeveloped airway structures can cause noisy breathing, poor nursing, milk from the nostrils, recurrent pneumonia, or poor growth in young horses.
Treatment cannot be selected by noise alone. Two horses that both “roar” may have different structures failing for different reasons. Endoscopic diagnosis under the conditions that reproduce the problem is central to making a useful treatment plan.
Contagious Respiratory Diseases
Fever, cough, nasal discharge, enlarged lymph nodes, and depression can look similar across several infections. The safest initial response is to treat an unexplained fever with respiratory signs as potentially contagious until a veterinarian advises otherwise.
Separate the horse, assign dedicated equipment, limit handlers, take and record temperatures, and stop unnecessary movement on and off the property. Use the fever in horses guide and the Infectious Disease Isolation Assistant to organize first steps while waiting for professional direction.
Equine influenza
Equine influenza is one of the most contagious respiratory infections of horses. The currently circulating equine influenza virus is influenza A, H3N8. It spreads through respiratory droplets and contaminated hands, clothing, buckets, tack, trailers, and other equipment. Crowding, travel, and the mixing of horses create ideal conditions for rapid transmission.
The incubation period is short, often one to three days. Typical signs include sudden fever, depression, poor appetite, enlarged lymph nodes, and a frequent, harsh cough. Nasal discharge often begins clear and may become thicker as inflammation continues or secondary bacterial infection develops. Vaccinated horses can have milder or less typical disease, so vaccination history does not rule it out.
Influenza damages the ciliated respiratory lining that normally clears mucus and debris. A horse may appear brighter before that lining has fully recovered. Returning to work too quickly can prolong coughing and increase the risk of secondary bacterial pneumonia.
Treatment is generally supportive and includes rest, good ventilation, hydration, palatable feed, and veterinary control of fever or complications. Antibiotics do not treat the virus and are reserved for suspected or confirmed bacterial involvement.
Vaccination reduces disease severity and spread but does not guarantee that an exposed horse will remain infection-free. The schedule should reflect age, travel, competition rules, vaccine product, and exposure risk. See the Horse Education Online guide to the equine influenza vaccine, the Vaccination Center, and the 5-Way Vaccine Planner for planning support.
Equine herpesviruses are widespread. EHV-1 and EHV-4 are the types most closely associated with respiratory disease. Young horses often show the clearest respiratory signs, including fever, watery nasal discharge, enlarged lymph nodes, poor appetite, and occasional cough. EHV-1 can also cause abortion, neonatal disease, and equine herpesvirus myeloencephalopathy, or EHM, a serious neurologic syndrome.
Herpesviruses can become latent after infection. A horse may carry the virus without signs and shed it again after stress or immune suppression. This makes control more complicated than simply identifying visibly sick horses.
PCR testing of nasal samples and, when EHV-1 is suspected, whole blood is commonly used during an outbreak. Results must be interpreted with the horse's signs, exposure history, and timing. Vaccines can reduce respiratory disease and viral shedding, and specific products help protect pregnant mares against EHV-1 abortion. Current vaccines are not labeled to prevent EHM reliably. Biosecurity and temperature monitoring remain essential.
The full Horse Education Online article on equine herpesvirus explains the respiratory, reproductive, and neurologic forms in more detail.
Strangles is caused by Streptococcus equi subspecies equi. It is a primary bacterial pathogen, meaning it can cause disease without a preceding viral infection or damaged airway. Young horses are affected most often, but a susceptible horse of any age can become ill.
Signs commonly begin with fever, depression, reduced appetite, and clear nasal discharge. The discharge becomes thicker as disease progresses. Lymph nodes under the jaw and behind the throat may become firm, painful, enlarged, and eventually abscess. Severe swelling can interfere with swallowing or breathing, which is the origin of the name “strangles.”
The disease spreads through direct contact with respiratory secretions and pus, as well as contaminated water, buckets, tack, clothing, hands, trailers, and other equipment. Horses can continue shedding after they look recovered. Some retain infected material or chondroids in the guttural pouches and become silent carriers.
PCR and culture may be performed on nasopharyngeal samples, abscess material, or guttural pouch lavage. Sample timing and location affect accuracy. Endoscopy is particularly useful when a carrier state is suspected.
Treatment depends on the stage and severity of disease. Many uncomplicated cases receive nursing care, soft feed, hydration support, pain and fever management, and attention to maturing abscesses. Antibiotic decisions require veterinary judgment. A horse in the earliest febrile stage is managed differently from an otherwise stable horse whose lymph nodes are already abscessing. Severe systemic illness, respiratory distress, dysphagia, aspiration pneumonia, or metastatic infection requires aggressive care.
Important complications include:
Guttural pouch empyema and chondroids
Airway obstruction from deep lymph-node abscesses
Aspiration pneumonia caused by difficulty swallowing
Internal abscesses, sometimes called metastatic or “bastard” strangles
Purpura hemorrhagica, an immune-mediated vasculitis that can cause extensive swelling and tissue damage
Septicemia, arthritis, neurologic disease, heart involvement, or severe muscle inflammation
Do not vaccinate a sick horse or make an outbreak vaccination decision without veterinary guidance. Previous infection, antibody level, product type, exposure status, and the risk of purpura all influence the plan. For a focused review, see Strangles in Horses: Symptoms, Isolation, Biosecurity, Vaccination.
Did You Know? A horse can look fully recovered from strangles and still carry S. equi in the guttural pouches. Identifying and treating carriers is often the step that finally ends repeated outbreaks on a property.
Equine viral arteritis and equine rhinitis viruses
Equine viral arteritis, or EVA, can cause fever, nasal discharge, cough, depression, and enlarged lymph nodes. Vasculitis may also produce swelling of the limbs, lower abdomen, sheath, or scrotum. The virus spreads through respiratory secretions during acute illness and through semen from carrier stallions. Important consequences include abortion and establishment of long-term infection in some sexually mature stallions. Breeding animals require coordinated testing, vaccination, recordkeeping, and semen-management protocols.
Equine rhinitis viruses A and B can be associated with fever, pharyngitis, cough, nasal discharge, lymph-node enlargement, and lower-airway inflammation. Their exact importance can be difficult to establish because viral material has also been found in some healthy horses. Diagnosis may involve PCR and paired antibody testing. Hygiene and general outbreak precautions remain the practical foundation of control.
Bacterial Pneumonia and Pleuropneumonia
Primary bacterial pneumonia is uncommon in healthy adult horses. It usually develops after normal respiratory defenses have been disrupted. Important risk factors include a recent viral infection, long-distance transport with prolonged head elevation, choke, difficulty swallowing, aspiration of feed or medication, general anesthesia, severe exercise, immune suppression, and advanced illness.
Bacteria that normally live in the upper airway or mouth can then reach and colonize the lower airways. Infection may begin around the bronchi as bronchopneumonia. If it extends through the lung and into the pleural space, the horse develops pleuropneumonia, a severe condition involving the lungs and the space around them. Mixed bacterial infection, including anaerobic organisms from the mouth, is common.
Signs include fever, depression, poor appetite, increased respiratory rate and effort, nasal discharge, and abnormal lung sounds. Cough may be present, but horses with pleural pain sometimes avoid coughing or taking a deep breath. They may stand with the elbows held away from the chest, appear stiff, resist movement, or grunt. After shipping, the condition is sometimes called shipping fever, although the problem is bacterial pleuropneumonia rather than fever alone.
Diagnosis commonly combines bloodwork, thoracic ultrasound, radiographs, and a sterile transtracheal sample for cytology and aerobic and anaerobic culture. Pleural fluid is sampled when present. Ultrasound helps determine the amount and location of fluid, fibrin, consolidated lung, or peripheral abscesses. Radiographs can reveal disease deeper in the chest.
Treatment may require broad initial antimicrobial coverage followed by adjustment based on culture, drainage of pleural fluid, pain control, intravenous fluids, oxygen, nutritional support, and frequent imaging. Thick fibrin can divide the pleural space into pockets, making drainage difficult. Some chronic or poorly resolving cases require surgery to remove necrotic tissue and establish drainage.
Complications include pulmonary abscesses, pneumothorax, pleural adhesions, bronchopleural fistulas, pulmonary infarction, laminitis, jugular thrombophlebitis, medication-associated colitis, and prolonged loss of condition. Early recognition and treatment improve both survival and the chance of returning to work.
Aspiration pneumonia
Aspiration deserves separate emphasis because owners may see the event that creates the risk. A horse with choke, impaired swallowing, milk or feed from the nostrils, neurologic disease, severe weakness, or an incorrectly placed tube may inhale contaminated material. Chemical irritation and bacterial infection can follow.
Do not force feed, drench, syringe medication, or offer large amounts of water to a horse that cannot swallow normally. Keep the horse's head low if it can do so safely, remove access to feed, and call the veterinarian. Respiratory signs may appear during the event or develop later, so follow-up monitoring is important even after the obstruction seems to have cleared.
Equine Asthma
Equine asthma is the current umbrella term for chronic, noninfectious lower-airway inflammation. Older terms include inflammatory airway disease, recurrent airway obstruction, chronic obstructive pulmonary disease, and heaves. Current terminology divides the condition into mild-to-moderate and severe equine asthma.
Horses with mild-to-moderate asthma may be any age and often look normal at rest. Poor performance, an occasional cough, and excess tracheal mucus may be the only signs. BAL cytology can show increased inflammatory cells, and specialized pulmonary testing may detect airway dysfunction that is otherwise easy to miss.
Severe equine asthma is more common in mature horses. Affected horses may cough frequently, produce nasal mucus, flare their nostrils, and use the abdominal muscles to force air out. Advanced cases struggle to breathe at rest. Permanent airway remodeling can develop over time, so a horse may improve clinically without returning to completely normal lung structure.
The two categories share features, but there is insufficient evidence to assume every mildly affected horse will progress to severe asthma. Infection must also be ruled out before the asthma label is applied.
Dust and organic material in the breathing zone are major triggers. Hay, straw, mold spores, mites, bacterial endotoxins, ammonia, arena dust, road dust, sweeping, and blowers can all contribute. Round bales are a particular concern because horses place their noses deep into a dusty feeding pocket. Some horses develop summer pasture-associated severe asthma and worsen outdoors during hot, humid periods when pollen and fungal exposure are high.
Environmental control is the foundation of treatment. Depending on the horse's triggers, changes may include more turnout, better ventilation, low-dust bedding, steamed or appropriately soaked hay, a complete pelleted or cubed forage alternative, removal of overhead hay storage, and taking the horse out while stalls or aisles are cleaned. Horses with pasture-associated disease may instead need to come off pasture during high-risk conditions. Forage changes must still meet the horse's nutritional needs and should be planned with the veterinarian or an equine nutrition professional.
Corticosteroids reduce airway inflammation. Bronchodilators relax constricted airway muscle and can provide rapid relief, but they do not control the underlying inflammation.
Medication cannot compensate for continued exposure to the trigger. Inhaled products may deliver medication directly to the respiratory tract, while systemic medication may be selected in more severe cases. All carry considerations involving dose, duration, competition rules, and adverse effects, so treatment must be veterinary directed.
Did You Know? In an asthmatic horse, the air around the nostrils matters more than dust on distant rafters. Hay particles, bedding, ammonia, and activity near the horse's face determine what reaches the airway with every breath.
Exercise-Induced Pulmonary Hemorrhage
Exercise-induced pulmonary hemorrhage, or EIPH, is bleeding from small pulmonary blood vessels during strenuous exercise. It occurs across high-intensity disciplines and is especially common in racehorses. The extreme pressure difference across the delicate blood-gas barrier can cause capillary stress failure, most often in the back and upper areas of the lungs.
Visible blood at the nostrils occurs in only a small percentage of affected horses. Many episodes are hidden and are found by endoscopy after exercise. BAL may reveal red blood cells or hemosiderophages, macrophages that contain iron left from earlier bleeding. Severe or repeated EIPH is associated with reduced performance and can contribute to scarring and vascular remodeling.
Furosemide has the strongest evidence for reducing the severity of EIPH in racehorses, but it does not eliminate bleeding. Its use is restricted or prohibited in some competitions and jurisdictions. Management must follow veterinary guidance and current governing-body rules. Evidence for many supplements, bronchodilators, anti-inflammatory drugs, and so-called capillary-strengthening products is limited or absent. Horse Education Online examines those claims in What Is Horse Capillary Strength Powder and Does It Work?.
Less Common but Important Lung Diseases
Pulmonary abscesses may follow aspiration or severe pneumonia. In foals and weanlings, Rhodococcus equi is an important cause of abscess-forming pneumonia. Young horses can compensate surprisingly well, so increased respiratory rate, fever, cough, poor growth, or reduced activity should not be ignored.
Interstitial pulmonary disease damages the tissue supporting the alveoli and can make the lungs stiff. Horses often develop rapid, shallow breathing, low blood oxygen, exercise intolerance, cough, fever, or weight loss. Causes include toxins, smoke or chemical inhalation, infection, and sometimes an unidentified trigger. Equine multinodular pulmonary fibrosis, or EMPF, is a progressive fibrotic disease strongly associated with EHV-5. Diagnosis may require radiographs, BAL, PCR, and lung biopsy. Adult horses with advanced interstitial disease generally have a guarded prognosis.
Fungal pneumonia is rare and often occurs in horses with severe gastrointestinal disease, immune suppression, neutropenia, or overwhelming exposure. Fungal spores are common in normal equine environments and may appear in respiratory samples without causing disease. Diagnosis therefore requires agreement among the horse's condition, imaging, cytology, culture, and sometimes tissue biopsy. Treatment can be prolonged, expensive, and potentially toxic.
Parasitic pneumonitis can occur when roundworm larvae migrate through the lungs of foals or when horses are exposed to lungworm carried by donkeys or mules. Cough, poor condition, nasal discharge, and abnormal lung sounds may resemble bacterial or inflammatory disease. Fecal testing can miss migrating larvae or lungworm in horses, so airway cytology and exposure history may be important. Use a veterinarian-directed parasite-control program rather than automatically repeating dewormers. The Equine Deworming Schedule Planner supports age- and risk-based planning.
Respiratory tumors are uncommon. Primary lung tumors are rarer than cancers that spread to the chest from another site. Chronic cough, weight loss, fever, exercise intolerance, pleural fluid, nosebleeds, or failure to respond to appropriate asthma or pneumonia treatment can raise suspicion. Granular cell tumors, lymphoma, and hemangiosarcoma are among the possibilities. Imaging and tissue or fluid analysis are usually needed, and prognosis depends on tumor type and extent.
Rare geographic diseases also belong in the veterinarian's differential list when travel or import history fits. African horse sickness is an insect-borne, reportable foreign animal disease that has never been detected in the United States. Hendra virus is an uncommon but highly dangerous zoonotic disease associated with flying foxes in Australia. Suspected cases require immediate official biosecurity procedures and should never be handled as routine respiratory illness.
Preventing Respiratory Disease
No plan prevents every respiratory problem, but good management reduces both exposure and delay in recognition.
Learn each horse's normal temperature, pulse, respiratory rate, and breathing effort.
Record cough, discharge, travel, medication, vaccination, and changes in performance.
Use a veterinarian-designed vaccination program based on age, use, location, travel, breeding status, and outbreak risk.
Isolate new arrivals and monitor temperatures before introducing them to the resident group.
Separate a horse with fever or unexplained respiratory signs immediately.
Do not share water, feed containers, tack, grooming tools, or nose-contact equipment during a disease concern.
Improve ventilation and reduce dust at the horse's breathing level.
Remove horses before sweeping, blowing aisles, shaking bedding, or moving hay.
Avoid moldy forage and bedding, and manage ammonia through frequent cleaning and airflow.
Allow horses to lower their heads during safe portions of long transport and provide appropriate travel breaks.
Address choke, swallowing problems, and dental disease promptly.
Use targeted parasite control, including appropriate management of donkeys and mules sharing the property.
Follow veterinary instructions for rest and gradual return to work after infection, pneumonia, asthma exacerbation, or pulmonary hemorrhage.
Vaccines are one layer of protection. Biosecurity, ventilation, early isolation, and reliable records remain necessary even in a well-vaccinated barn. The Horse Vaccination Center and 5-Way Vaccine Planner can help owners prepare for a veterinarian-led vaccine discussion.
Prognosis and Return to Work
Outcome depends on the cause, disease severity, time to treatment, and the amount of permanent tissue damage. Influenza and uncomplicated strangles often resolve with proper care, but premature exercise can delay recovery. Early bacterial pneumonia can respond well, while established pleuropneumonia may require weeks or months of treatment. Equine asthma can often be controlled, but recurrence is likely if triggers return. Structural obstructions may respond well to surgery when the correct lesion is identified. Advanced fibrosis, extensive cancer, severe aspiration, or prolonged respiratory failure carries a more guarded outlook.
Return-to-work decisions should be based on the diagnosis rather than the disappearance of fever alone. The respiratory lining, lung tissue, and overall condition may need additional time to recover. A gradual plan allows the veterinarian and owner to monitor respiratory rate, cough, noise, recovery time, and performance before intensity increases.
Conclusion
The same sign can have very different causes, so diagnosis must come before treatment. Owners help most by recognizing changes early, isolating when infection is possible, recording useful details, and involving the veterinarian before respiratory disease becomes advanced.
Frequently Asked Questions
1. Can a horse have respiratory disease without coughing?
Yes. Mild asthma, EIPH, dynamic upper-airway obstruction, early pneumonia, and some tumors can reduce performance or increase respiratory rate without obvious coughing.
2. Is clear nasal discharge normal in a horse?
A little clear discharge can appear briefly after exercise or in cold air. Persistent, one-sided, or heavy discharge, especially with fever or cough, deserves investigation.
3. What does discharge from only one nostril mean?
It may indicate sinusitis, dental-root infection, a mass, a foreign body, or guttural pouch disease. Endoscopy and imaging may identify the cause.
4. When is a horse's cough an emergency?
Seek urgent advice with breathing difficulty, high fever, nasal feed or saliva, marked depression, chest pain, blood, or similar illness in several horses. Persistent cough also warrants examination.
5. Is equine asthma contagious?
No. It is inflammatory and does not spread between horses. Infection can look similar, especially with fever, new discharge, or several affected horses.
6. Are heaves and equine asthma the same condition?
Heaves is the older name for severe equine asthma. Mild-to-moderate asthma causes subtler inflammation, often seen as occasional cough or poor performance.
7. Will antibiotics stop a horse from coughing?
Only when appropriate for a bacterial infection. Antibiotics do not treat influenza, asthma, EIPH, or structural obstruction, and unnecessary use promotes resistance.
8. Should a coughing horse be isolated?
Isolate first when the cause is unknown and there is fever, discharge, recent exposure, or illness in barnmates. Adjust after veterinary assessment.
9. How long should a horse rest after a respiratory infection?
There is no universal schedule. Diagnosis, fever, airway damage, fitness, and workload matter. Return gradually after significant signs resolve and the veterinarian approves.
10. Can barn changes really control equine asthma?
Yes. Reducing dust, mold, endotoxin, and ammonia is central. Medication helps control inflammation and narrowed airways, but signs often return with trigger exposure.
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