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Pneumonia in the adult horse

Alexandra Moss, BVSc

Early recognition and appropriate treatment are keys to a successful outcome in cases of 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 susceptible 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, adult horses can still be affected with pneumonia. Pneumonia is most often seen in older horses that have pre-exiting illnesses or a history of transport or other factors that may make them more susceptible to the disease.

Preventing pneumonia

Pneumonia is not usually contagious between horses unless a group of horses has been exposed to the same virus or other illnesses that makes them all vulnerable. Therefore, the most important considerations in preventing pneumonia are good management:


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:


Treatment of mild to moderate cases of pneumonia can be successful, and typically includes antibiotics, anti-inflammatories, and supportive care. But in more severe cases, treatment can be challenging as permanent damage can be done to the lung tissue. The long-term performance of the horse may be affected 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 herpesvirus infection, equine influenza and equine viral arteritis.

Signs of viral respiratory infections include:

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

Secondary bacterial respiratory infections are most frequently caused by bacteria that live in the upper respiratory tract of the horse. These secondary infections do not always result in pneumonia, but can when they are more severe.

Secondary bacterial infection symptoms include:

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:

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


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