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Pneumonia in the adult horse

Quick facts

  • Pneumonia is a respiratory infection that’s generally not contagious to other horses.
  • Signs of pneumonia include nasal discharge, fever and depression.
  • Practicing biosecurity, vaccinating against respiratory infections and managing chronic illnesses can help prevent pneumonia in your horse.

What is pneumonia?

Pneumonia is an infection in the lungs that may be caused by bacteria, virus, fungus and/or aspiration.

Foals develop pneumonia more commonly than adult horses. They are more prone to bacterial infections and are at a higher risk for developing aspiration pneumonia, which can occur when food, saliva, or liquid is breathed into the lungs instead of being swallowed.

However, pneumonia can still affect adult horses. Pneumonia is most often seen in older horses that have pre-existing illnesses or a history of transport or other factors that may make them more prone to the disease.

Preventing pneumonia

The most important considerations in preventing pneumonia are good management:

  • Minimize stress, particularly when mingling with other horses or transporting horses over long distances. Break up long trips, maintain good security when away from home and keep to a regular routine.
  • Check with your veterinarian if pre-existing conditions may make your horse vulnerable to pneumonia. Examples include Cushing’s disease, Equine Metabolic Syndrome and Inflammatory Airway Disease.
  • Maintain management of other previously diagnosed illnesses.
  • Stay up-to-date on vaccinations to protect against common respiratory infections.
  • Be aware of the possible signs of pneumonia.

Signs of illness

Pneumonia isn’t usually contagious between horses unless a group of horses has been exposed to the same virus or other illness that makes them all vulnerable. Signs of pneumonia vary with the type of pneumonia a horse has. Please see the types of pneumonia below for more specific signs.

Possible signs of pneumonia include:

  • Yellow- or cream-colored nasal discharge
  • Depression
  • Persistent fever


Diagnosis of pneumonia, and determining the exact cause, requires a thorough work-up so your veterinarian can prescribe the most appropriate therapy. Diagnostic tests can include:

  • Blood work (CBC and biochemistry panels) to determine the severity of systemic illness.
  • Thoracic ultrasound to visually assess the extent of damage on the lung surface.
  • Trans-tracheal wash to collect a sterile fluid sample from the lungs that can be submitted for culture and sensitivity.
  • Culture and sensitivity to determine the exact pathogen responsible for the pneumonia and it’s sensitivity to different types of antibiotics.


Treatment of mild to moderate cases of pneumonia can be successful, and typically includes antibiotics, anti-inflammatories, and supportive care. In more severe cases, treatment can be challenging as permanent damage can be done to the lung tissue. Pneumonia may affect the long-term performance of the horse depending on how much of the lung tissue is permanently affected.

Types and causes of pneumonia

Viral pneumonia

The most common type of respiratory infection in horses is viral. Most frequently, they may contract equine herpes virus infection, equine influenza and equine viral arthritis.

Signs of viral respiratory infections include:

  • Fever
  • Clear nasal discharge
  • Swelling of the lymph nodes in the throat area
  • Poor appetite
  • Cough

Viral infections seldom cause pneumonia on their own. A virus can primarily contribute to the development of pneumonia by causing the respiratory system to become vulnerable to a secondary bacterial infection.

Bacterial infection

Bacteria that lives in the upper respiratory tract of the horse are the most frequent cause of secondary bacterial infections. These secondary infections do not always result in pneumonia, but can when they are more severe.

Secondary bacterial infection symptoms include:

  • Yellow or cream-colored nasal discharge
  • Depression
  • Persistent fever
  • Previously mentioned viral symptoms

Shipping pleuropneumonia

Shipping pleuropneumonia can occur when horses are put under stress of being transported and mixed with new horses. This can be a severe condition when both the lungs and the surrounding (pleural) cavity become affected. Therefore, in addition to other signs seen with pneumonia, in cases of shipping pleuropneumonia the horse may:

  • Stand with their elbows camped out
  • Lie down more often
  • Be reluctant to move

Pneumonia can also develop if your horse has an inflammatory airway disease, such as equine asthma.

Author: Alexandra Moss

Reviewed in 2024

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