Management measures such as switching to wood or paper bedding and steaming hay rations can cut down on the levels of fungi in a horse’s environment, reducing the risk of inflammatory airway disease (IAD), according to a study from Belgium.
“IAD is a milder form of respiratory disease, which does not translate into such severe signs as seen with recurrent airway obstruction (RAO), but which nonetheless reduces the horse’s breathing capacity and, as a consequence, his capacity to exercise and perform,” explains Emmanuelle van Erck-Westergren, DVM, PhD, of the Equine Sports Medicine Practice in Waterloo. “Some scientists think that IAD can be a precursor to RAO.”
The role of environmental dust in triggering respiratory disease is well documented, and one component of dust is fungi. To determine the role of fungi in the development of IAD, van Erck-Westergren and her colleagues collected data on 731 horses referred to their practice for respiratory disease or poor performance.
Each horse was given a full clinical exam, which included endoscopy of the airway, along with a tracheal wash and bronchoalveolar lavage to retrieve bacteria and fungi from the airways and lungs. The researchers also collected management information, including the type of bedding used and the forages that the horses were fed---dry hay, moistened hay, steamed hay or haylage. Hay was steamed using a commercial hay-steaming system designed for that purpose.
The data showed that 89 percent of the study horses had IAD. Overall, “fungal elements” were found in tracheal wash fluid of 81 percent of IAD-positive horses and 65 percent of non-IAD horses. Horses harboring fungal elements were about twice aslikely to develop IAD than were those who did not. These findings, the researchers say, support the idea that aerosolized fungal elements play a role in the development of IAD just as they do with RAO.
The researchers also identified management practicesthat can exacerbate or mitigate the effects of fungi on the horse’s respiratory system. The degree of lower airway inflammation, measured by the amount of white blood cells captured in the bronchoalveolar lavage, was significantly higher when horses were bedded on straw versus shavings, or when fed dry hay versus steamed hay.
Specifically, horses fed with dry hay had 2.7 times more chances of being diagnosed with IAD compared to those who received steamed hay. Steaming decreased the likelihood of finding fungal elements in tracheal washes by a factor of two. Soaking hay did not influence the findings of fungal elements.
van Erck-Westergren says that controlling a horse’s environment to help eliminate fungi can allow the horse to clear the organisms or spores present in his airways. “Inhalation with saline or scientifically tested essential oils can help accelerate clearance,” she adds. “When the fungi have started to proliferate within the airways [in a horse with decreased immunity or strong environmentalburden], anti-fungal treatment can be indicated.”
Reference: “Fungi in respiratory samples of horses with inflammatory airway disease,” Journal of Veterinary Internal Medicine, December 2018
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