Merck Manual

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Pet Owner Version

Aspiration Pneumonia in Horses


Philip R. Scott

, BVM&S, MPhil, DVM&S, DSHP, DECBHM, FHEA, FRCVS, University of Edinburgh

Reviewed/Revised May 2019 | Modified Oct 2022

Aspiration pneumonia is a lung infection caused by inhalation of foreign material. The severity of the inflammation depends on the material inhaled, the type of bacteria inhaled, and the distribution of foreign material in the lungs. A common cause of aspiration pneumonia is the improper administration of liquid medicines. If an animal needs to be given liquids through a drench or dose syringe, they should not be administered any faster than the animal can swallow. Animals that attempt to eat or drink while partially choked are at risk for aspiration pneumonia as well. Disturbances in the normal swallowing mechanism, such as in anesthetized or comatose animals, or in animals with deformities such as cleft palate, are frequent causes.

A history suggesting that a foreign substance might have been inhaled is the most important clue to diagnosing this disease. Signs include labored or rapid breathing, rapid heart rate, and fever. Other signs include bluish mucous membranes and airway spasms. A sweetish, off-smelling breath may be detected, which becomes more intense as the disease progresses. This is often associated with a nasal discharge that sometimes is tinged reddish brown or green. Occasionally, evidence of the breathed-in material can be seen in the nasal discharge or coughed-up material.

As with nearly all disease conditions, prevention is better than treatment. This is especially the case for aspiration pneumonia, since the outlook is poor even with treatment. The rate of death is high, and recovered animals often develop lung abscesses. If an animal is known to have inhaled a foreign substance, broad-spectrum antibiotics are usually prescribed without waiting for signs of pneumonia to appear.

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