equine asthma
Equine asthma (EA) affects the horse’s lower respiratory tract. However, it also seems to be associated with upper respiratory tract problems that become apparent during exercise.

Horses with EA are more likely to have physical abnormalities of the pharynx (an upper airway structure which extends from the rear of the mouth and nasal passages to the larynx and esophagus) during exercise their EA-free counterparts, Polish researchers found in a recent study. That could be because the way air flows through EA horses’ respiratory tracts causes higher negative pressure (pressure that’s lower than the surroundings) on the pharynx. Or it might be that a flawed pharynx is causing horses to inhale food materials, resulting in inflammation that leads to EA.

“There’s still some work left ahead of us to determine what’s causing what,” said Blanka Wysocka, PhD, of the Warsaw University of Life Sciences Faculty of Veterinary Medicine, in Poland.

In their study, Wysocka and her colleague carried out upper and lower airway exams—at rest and during work on a treadmill—in 13 horses with EA and 16 horses without. The treadmill allowed them to compare exercise-related conditions in a controlled environment, she said.

They found that more than 60% of the EA horses had structural changes in their throat during exercise, Wysocka said. At rest, they only identified abnormalities in 24% of the horses. The most common structural changes in these horses were related to the pharynx—specifically, soft palate instability and pharyngeal wall collapse.

However, horses without EA also had dynamic changes in the upper airway during exercise, she added. Nearly 70% of the horses without EA had issues, mostly relating to the larynx. Roaring—partial paralysis of the larynx—was the most common condition seen in these horses, said Wysocka. The reason for this distinction is unclear but might be related to the horses’ age (the EA horses in this study happened to be much younger than those without), she said; more research is needed to clarify why this phenomenon occurred.

Clinical examinations including endoscopy during treadmill work could give better clues about what’s causing poor performance in horses with EA. “It’s important to determine if the problems are coming from the upper airway or the lower airway or both,” Wysocka said.

Until more research can be carried out, Wysocka said she recommends owners of EA horses have their animals evaluated for signs of upper airway changes during exercise. If EA treatment doesn’t resolve the dynamic changes in the pharynx, owners might consider surgery to resolve the upper airway disorders as a complement to lower airway treatment, she said.

The study, “The occurrence of dynamic structural disorders in the pharynx and larynx, at rest and during exercise, in horses diagnosed with mild and moderate Equine Asthma (Inflammatory Airway Disease),” was posted in the Polish Journal of Veterinary Science.