Equine Asthma Research Update

Severity of equine asthma varies from horse to horse. Some show few clinical signs, while others possess a full spectrum of symptoms. Regardless of the severity of asthma, affected horses always have mucus accumulation notable on endoscopic examination of the airways.

“Based on the latest treatment guidelines^*, bronchodilators, systemic corticosteroids, omega-3 fatty acid supplementation, and allergen avoidance have been identified as the top methods of treating asthmatic horses,” said Catherine Whitehouse, M.S., a nutrition advisor for Kentucky Equine Research.

“Those guidelines suggested administering an omega-3 product like EO-3 , available from Kentucky Equine Research,” she added. EO-3 is capable of providing 1.5 g of DHA daily.

As pointed out by one researcher, equine asthma is a complex disease syndrome with a number of different faces^**. As such, managing asthmatic horses can be challenging and one treatment approach will not work with all horses.

Several novel treatment strategies have been described in the literature recently, including immunomodulatory nanoparticle administration and an allergy vaccine, which are still being researched and not yet clinically available. In contrast, other researchers recently explored the possibility of using azithromycin to help manage affected animal^***. Azithromycin, like other medications in the macrolide family of drugs, has antibiotic and immunomodulatory properties.

“Human studies show that prolonged administration of azithromycin improves lung function and airway inflammation,” Whitehouse said.

To determine if azithromycin was equally beneficial for horses, six asthmatic horses were administered either azithromycin (10 mg/kg orally once daily for 5 days then every other day for two additional doses) or ceftiofur, an antibiotic without immunomodulatory activity, as a control. The researchers found no improvement in lung function, tracheal mucus accumulation, bronchial remodeling, or airway neutrophilia (accumulation of neutrophils, a type of white blood cell) in either group.

“They did, however, identify decreased expression of the proinflammatory mediators interleukin-8 and interleukin-1β, both of which are involved in attracting neutrophils,” Whitehouse explained.

The researchers therefore concluded that “the decreased expression of neutrophilic chemoattractants by azithromycin is noteworthy considering the lack of medication reliably improving pulmonary inflammation in severe asthmatic horses.”

They also emphasized that the use of macrolides in asthmatic horses is not recommended at this time considering no improvement in lung function was observed and due to concerns surrounding antibiotic resistance and the potential for antibiotic-associated adverse events.

^*Couëtil, L.L., J.M. Cardwell, V. Gerber, et al. 2016. Inflammatory airway disease of horses—Revised consensus statement. Journal of Veterinary Internal Medicine. 30(2):503-515.

 ^**Montgomery, J.B. 2019. Beyond steroids and bronchodilators: Investigating additional therapies for horses with severe equine asthma. Veterinary Record. 185(5):140-142.

 ^***Mainguy-Seers, S., A. Vargas, O. Labrecque, et al. 2019. Randomised study of the immunomodulatory effects of azithromycin in severe asthmatic horses. Veterinary Record. 185(5):143.