Newly released three-year study cites steamed hay as critical to preventing inflammatory airway disease, a stealth equine ailment that affects more than 80 percent of horses

Inflammatory Airway Disease affects huge numbers of horses and often goes undetected while impacting their performance. A three-year research project published by The Journal of Veterinary Internal Medicine expands extensive past research confirming IAD’s prevalence. Conducted by a group of equine sports medicine veterinarians in Belgium, new research studied more than 700 active sport horses referred for performance issues or possible respiratory problems—88 percent were diagnosed with IAD.

The study also cited steamed hay, such as Haygain, as critical to preventing IAD—horses fed steamed hay were 65 percent less likely to develop the condition than those fed dry hay. Led by Dr. Julie Dauvillier, the study is the first to connect fungi in the horse’s respiratory system with high incidence of IAD. Along with many inhalable irritants, fungi are present in even top quality hay. High-temperature hay steaming kills fungi, hence its effectiveness in preventing IAD.

“This paper highlights a major piece of the puzzle of equine airway diseases—the role of fungi,” said Dr. Van Erck-Westergren, co-author of the study. “In human medicine, fungi are known to cause many respiratory inflammatory conditions such as allergies, infection and asthma. In equine veterinary medicine, we can find publications that relate the role of fungi in pretty nasty, potentially life-threatening diseases such as fungal pneumonia or guttural pouch mycosis, but barely anything else. Our paper shows for the first time that ubiquitous molds, including fungi, cause chronic lower airway inflammation which is deleterious for the health and performance of our horses.”

Along with dry hay, straw bedding had a high correlation to IAD incidence. The study also found that soaking hay, haylage and “dust-free” hay did not reduce the risk of fungi-related IAD, while wood shavings were deemed the best option for stalls that require bedding.

Fungi Found Everywhere

“Fungal spores naturally contaminate hay and straw during harvest,” the study’s authors explained. “The degree of contamination and proliferation is directly related to harvesting practices, initial levels of soil contamination, as well as storage conditions.”

IAD is a stealth illness. It sometimes presents with an occasional cough and mild nasal discharge but often lurks without symptoms. Unexplained decreases in performance are complaints that often lead to bronchoaveolar and trachea washes that reveal an IAD diagnosis. Unmanaged, this condition will progress and potentially mean these horses are more susceptible to debilitating extremes of the equine asthma spectrum, including recurrent airway obstruction, or “heaves.”

“A link between fungal growth and an immunodepressive state could not be demonstrated in our study,” the authors noted. “However, it is likely that the immune system of some of the horses included in our study would have been challenged by intensive training, regular transport and competition.”

Finding fungi in so many horses’ respiratory tracts caused the authors to question the “use of corticosteroids as a unique treatment of airway inflammation” because they depress the immune system, which actually fights the fungal infection. They noted that anti-fungal treatment is included in prescriptions for human allergic diseases involving a fungal component, like severe acute respiratory syndrome. Perhaps it should be for horses, too.

Environmental Solutions

“Environmental management is the only way to protect your horse against fungi,” explained Dr Van Erck-Westergren in a follow-up interview. “Fungi are everywhere—in the straw, in the hay and in the stall and storage areas. Their aim is to proliferate. There is now overwhelming evidence for the effectiveness of Haygain steamed hay in reducing IAD and helping to improve respiratory health in horses.”

Regular stall disinfection, dust-free shavings and a sealed flooring system that requires minimal bedding, such as ComfortStall, were additional recommendations for keeping fungi at bay, preventing IAD and maintaining overall respiratory health.

To read the complete study “Fungi in Respiratory Samples of Horses with Inflammatory Airway Disease,” visit

For more information on Haygain USA, visit Article provided courtesy Haygain USA.


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