Forage and bedding harbor molds and fungi that pose health hazards to horses. When fungi are in contact with the respiratory lining, they cause an inflammatory response and also can potentially produce mycotoxins that add to the respiratory insult.
At the 2019 AAEP Convention, Emmanuelle van Erck Westergren, DVM, PhD, DECEIM, discussed the significance of fungi on the respiratory tract and performance. The study was based on ambulatory practitioners’ examination of horses with poor performance or respiratory problems between 2013-2016. As ambulatory veterinarians, these practitioners were not only able to examine the horses, but they also could evaluate environmental factors on site and how those factors might be a risk to respiratory health.
Of 732 horses, 721 were housed indoors and 646 (88%) had inflammatory airway disease.
Fungal elements were identified in 81% of respiratory samples taken from the trachea or lower airways.
A horse with fungal elements had two times more risk of inflammatory airway disease than horses with no fungal elements in their respiratory samples.
Most horse owners’ clinical complaints centered on poor performance, yet the horses did not necessarily have a cough. Horses with signs of fungal proliferation (seen on cytologic exam of respiratory samples) experienced cough and epistaxis (bloody nose) more frequently.
Environmental risk factors are important to the development of fungal respiratory irritation—straw has a higher incidence of fungal exposure than shavings; soaked hay has a greater incidence than dry hay, and dry hay provides twice the fungal exposure of haylage or steamed hay. (The hay study concluded that hay steamed at high temperatures significantly decreased the risk of fungal exposure.)