Researchers from the University of Montreal recently discovered a link between equine respiratory tract innervation and severe asthma in horses. These findings might open doorways to some new approaches to managing this condition.

Equine asthma is a common disease affecting up to 15% of adult horses. Cases can vary in severity from mild exercise intolerance to severe respiratory disease at rest, and, at its worst, asthma can dramatically affect a horse’s quality of life. It can be difficult for owners and veterinarians to fully control the condition, and treatment is often costly or not feasible. Currently there is no cure, meaning this is a lifelong management problem for owners and veterinarians.

Led by Laurence Leduc, DVM, Dipl. ACVIM-LA, the researchers examined lung tissue samples collected from eight healthy horses and eight horses with a confirmed diagnosis of severe equine asthma (including both actively affected horses and horses in remission). They marked the nerve tissue within the lungs to calculate the amount of innervation and compare that of the affected and healthy horses. From this, the researchers determined the horses with severe asthma did have significantly more innervation in their lungs than the healthy horses.

These findings suggest that horses with asthma likely have more reactive airways, meaning they might start spasming or become inflamed when challenged with smaller amounts of a trigger (dust, pollen, etc.) compared to unaffected horses. “We now know that airway innervation could be involved in its development and persistence,” says Jean-Pierre Lavoie, DVM, Dipl. ACVIM, contributing author and researcher on the study. “The increased nerve supply to the airway smooth muscle we observed may play a critical role in equine asthma, (and) therapies targeting airway nerves may eventually emerge from the findings of our study.” 

Veterinarians already use treatments targeting some airway innervation in horses with asthma, says Lavoie—bronchodilators. “In humans, interventional therapies, including bronchial thermoplasty and targeted lung denervation, are emerging as potential avenues to address the altered airway innervation observed,” he explained. “These therapies could eventually be investigated in horses.”

Future Equine Asthma Research

“Our next objective is instead to determine the reversibility of the increased innervation to ascertain the length of time required for the altered airway innervation to improve or resolve, if at all,” said Lavoie. “To achieve this, we will compare the airways of asthmatic horses in remission and exacerbation (asthma crisis) over time.”

The study, Severe Asthma in Horses is Associated with Increased Airway Innervation, appeared in the Journal of Veterinary Internal Medicine in January, 2024.