Respiratory Relief in Horses: Reach for Salbutamol        

Horses in acute exacerbation of severe equine asthma (SEA) typically require a bronchodilator for their comfort. When comparing the bronchodilators salbutamol and hyoscine butylbromide (HBB), they have equivalent potency, but salbutamol lasts longer and has a better safety profile.^*

According to the most recent guidelines, key management strategies for equine asthma include:

• Environmental and dietary control to minimize exposure to allergens;
• Corticosteroid anti-inflammatory drugs;
• Bronchodilators; and
• An omega-3 fatty acid supplement such as EO-3 from Kentucky Equine Research.

“Long-chain omega-3 fatty acids may have a protective role in equine asthma by supporting immune and lung health. EO-3, a marine-derived fish oil, contains EPA and DHA, making it an effective supplement to balance the omega-6 to -3 ratio in the diet and body tissues,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

The airways of SEA horses become obstructed by inflammation, bronchoconstriction, mucus accumulation, and structural changes (e.g., increased airway wall thickness of the airways due to muscle hypertrophy).

Bronchoconstriction, a narrowing of the horse’s airways, can be rapidly improved with bronchodilators. Salbutamol is a β2 adrenergic agonist, and HBB is an anticholinergic. HBB, also used for pain control in colicky horses, is known to cause increased heart rates. For this reason, HBB is contraindicated in horses with underlying primary cardiac disease. HBB can also decrease intestinal motility. Salbutamol, however, is not associated with these adverse effects.

Canadian veterinarians specializing in asthma research recently compared the potency and duration of action of both salbutamol and HBB.^* They hypothesized that HBB would be more potent but that benefit might be outweighed by the adverse effects.

Six horses with a history of severe asthma in acute asthma exacerbation through environmental challenge were treated with either salbutamol (1,000 µg delivered by an inhalation chamber) or HBB (150 mg intravenously). Lung function (i.e., resistance and reactance), heart rates, and gastrointestinal sounds were evaluated at baseline immediately before administering the medications and intermittently for 180 minutes thereafter.

“Both bronchodilators resulted in a rapid alleviation of airway obstruction. But, contrary to the researchers’ hypothesis, both medications had similar potencies. Bronchodilation lasted longer with salbutamol and horses treated with salbutamol had fewer adverse effects than HBB-treated horses; however, individual responses to treatment were observed,” said Whitehouse.

Heart rate in the HBB group increased 13 beats/minute whereas heart rates in the salbutamol-treated horses only increased 3.3 beats/minute. Gastrointestinal sounds decreased in the HBB group more than in the salbutamol group.

The researchers concluded, “Gastrointestinal and cardiovascular effects were noted only with HBB, suggesting the preferential use of salbutamol to relieve bronchoconstriction in horses with asthma.”

^*Mozo Vives, B., S. Mainguy-Seers, and J-P. Lavoie. 2024. Comparative study of the bronchodilator efficacy and adverse effects of salbutamol and hyoscine butylbromide in horses with severe asthma. Journal of Veterinary Internal Medicine:17057.