The use of straw for bedding and the feeding of dry hay cannot be recommended for performance horses, according to the authors of a just-published study.
Both were significant risk factors for inflammatory airway disease (IAD) in horses and ramped up the risk of fungal elements being present in their airways, they reported.
Julie Dauvillier, Fe ter Woort and Emmanuelle van Erck‐Westergren, all with the Equine Sports Medicine Practice in Waterloo, Belgium, have described their findings in the Journal of Veterinary Internal Medicine.
Fungi are known to contribute to the inflammatory response of lungs in horses with recurrent airway obstruction (RAO) and in some forms of asthma in humans.
However, the role of fungi have not been assessed in IAD, a condition characterized by a cough, poor performance, and excess mucus within the airways, which can often be seen during an endoscopy.
The trio set out to evaluate the prevalence of fungi in respiratory samples from horses diagnosed with IAD, describe clinical signs associated with fungi in respiratory samples, and assess the risk factors associated with the condition.
The study involved 731 horses referred to a specialized mobile practice for signs of respiratory disease or poor performance.
The horses, active in sport, racing, and leisure, were referred for respiratory disease, for decreased performance, or, in some cases, for a routine seasonal examination without any clinical complaint.
The researchers collected clinical data, observed environmental conditions, and conducted a tracheal wash and bronchoalveolar lavage. Samples were examined under a microscope for signs of problems, and efforts were made to culture fungi and bacteria from the tracheal samples.
Positive fungal cultures were obtained in 55% (402/731) of the horses.
Horses with fungal elements observed in their tracheal wash samples were twice as likely to have IAD as horses without fungi.
The risk of being diagnosed with IAD and the likelihood of fungi in the tracheal wash were higher when horses were bedded on straw, or fed dry hay.
Horses fed with dry hay were found to be 2.6 times more likely to have fungal elements in their tracheal wash samples.
Horses fed with steamed hay had 65% reduced odds of being diagnosed with IAD.
Distinctive respiratory clinical signs linked to the presence of fungi included a cough, breathlessness, or a nasal discharge.
Horses bedded on wood shavings had 40% reduced odds of having fungal elements in their tracheal wash and a 30% lower risk of being diagnosed with IAD in comparison to horses on other bedding types.
Conversely, horses housed on straw had 90% increased odds of having fungal elements in their tracheal wash.
The most commonly isolated fungi was Penicillium (53%), Aspergillus (34%), Rhizomucor (5%), and Candida (5%).
Penicillium and Aspergillus are airborne and common, classically found in stable air. Aspergillus is the most commonly isolated fungi in hay.
“Our study demonstrates that fungal elements are commonly present in equine airways and that horses inhaling aerosolized fungal particles are at a significantly higher risk of having IAD,” they concluded.
The findings, they said, pointed to the role that aerosolized fungal elements played in IAD.
Fungi can be allergenic, infective, toxic, or any combination of the above; and their role in equine IAD needs to be further investigated, they said.
“Although fungi might not necessarily be the primary cause of IAD, it is possible that deficits in immunity might modify the equine ability to react to infection.”
They said the high frequency of fungal particles in the airways of horses raised the question of the safety of use of corticosteroids as a unique treatment of airway inflammation and the risks of promoting fungal growth by depressing the immune response in the airways.
The researchers found no relationship between a positive bacterial culture in tracheal washes and the presences of IAD.
“In our study, straw bedding and dry hay feeding represented significant risk factors for IAD and for the presence of fungal elements in equine airways. Their use cannot be recommended in performance horses.
“Fungal spores naturally contaminate hay and straw during harvest.
“The storage of hay and straw can also lead to an exponential increase in fungal proliferation within the batches.”
The degree of contamination and proliferation is directly related to harvesting practices, initial levels of soil contamination, as well as storage conditions.
“On the contrary, wood shavings decreased the risk of IAD and the detection of fungal particles in the airways. This bedding type seems to be an appropriate solution to maintain equine respiratory health.
“The use of high‐temperature hay steaming also had a significantly protective effect against the development of IAD and the contamination of airways with fungal particles in our study.
“Interestingly, soaking the hay, which is often recommended as a protective measure for horses with respiratory inflammation, did not significantly decrease the risk of being IAD nor the risk of having fungal elements in the airways.
“Similarly, the use of haylage did not reduce the risk of IAD in our study.”
Fungi in respiratory samples of horses with inflammatory airway disease
Julie Dauvillier, Fe ter Woort and Emmanuelle van Erck‐Westergren
Journal of Veterinary Internal Medicine, December 21, 2018; https://doi.org/10.1111/jvim.15397