Respiratory

Tracheal wash offers little actionable information for treating asthmatic horses

By Adam Marcus

The presence of bacteria in a tracheal wash from a horse with asthma frequently is unrelated to the presence or absence of a respiratory infection. Therefore, on its own it should not dictate treatment plans, researchers have found.

The results of a recent study suggest some horses with asthma may be receiving antibiotics unnecessarily, potentially promoting the development of resistance to the drugs.

“Although positive tracheal wash cultures were common, they were not associated with more severe airway inflammation and remodeling, or even with the presence of bacteria or infection in bronchial tissues,” said Laurence Leduc, DVM, an expert in equine asthma at the University of Montreal, who co-led the research with her colleague, Jean-Pierre Lavoie, DMV. “This suggests that the presence of bacteria lining the airways does not necessarily drive disease severity in horses with asthma. Overall, our study reinforces that the main focus in equine asthma management should remain on reducing airway inflammation and environmental dust exposure rather than on antimicrobial treatment.”

During exacerbations of asthma, horses often develop symptoms like shortness of breath, cough, nasal discharge and even fever that can lead veterinarians to suspect a secondary bacterial infection. In cases when a tracheal wash culture is performed, a positive result often prompts the use of antibiotics, according to Dr. Leduc.

A survey published in 2024 of nearly 250 equine veterinarians in 25 countries found more than half said they prescribed antimicrobial agents in cases of asthma (Animals 2024;14[3]:457).

For this study, which appeared in a recent issue of the Equine Veterinary Journal, Dr. Leduc and her colleagues analyzed tracheal wash samples from 31 horses, of whom 13 had severe asthma, 9 had moderate asthma and 9 were considered healthy. Cultures from the washes were positive for bacteria in 8 of the animals with severe asthma, 6 of those with moderate asthma, and 8 with normal airways.

Histology from endobronchial biopsies, cytology assessments of bronchoalveolar lavage fluid and tracheal mucus did not differ among the horses with asthma with and without positive wash cultures.

“When concurrent bacterial pneumonia is suspected in horses with asthma, which is uncommon, veterinarians should rely instead on additional findings, such as complete blood count, inflammatory markers and thoracic imaging,” Dr. Leduc told The Modern Equine Vet. “Until proven otherwise, the cornerstone of treatment in horses with asthma should remain environmental management, corticosteroids during the acute phase, and bronchodilators when needed.” MeV

FOR MORE INFORMATION
Leduc L, St-Jean G, Lavoie JP. Tracheal wash culture is not associated with bronchial infection, remodelling or inflammation in horses with asthma. Equine Vet J. 2026 March 17.
https://doi.org/10.1002/evj.70157