Field-applicable low-intensity exercise induces bronchodilation in horses with severe asthma.

Abstract

BACKGROUND: Airway dysfunction in severe equine asthma (SEA) often results in early retirement or euthanasia of affected horses. Exercise-induced bronchodilation occurs in horses with SEA after intense treadmill exercise, but the effects of a lighter, field-applicable, training regimen remain largely unexplored. OBJECTIVES: To evaluate the impact of submaximal aerobic exercise on airway obstruction during exacerbation of SEA. STUDY DESIGN: The preliminary phase explored the effects of a 25-min standardised exercise on the lung function of eight SEA horses. As notable bronchodilation occurred, the results were confirmed in a randomised controlled crossover protocol comparing the effect of the same standardised exercise on lung function with that of an equal duration turnout. METHODS: Lung function was assessed by standard lung mechanics before and 15 min after the interventions (turnout and walk/trot lungeing exercise). To compare exercise-induced bronchodilation with that of a potent bronchodilator in the main study, salbutamol was administered after the turnout intervention only, and lung function was measured again 5 min later. Data were analysed with t tests, Wilcoxon tests, and mixed-effects models. RESULTS: In the preliminary phase, exercise led to a mean 50% reduction in pulmonary resistance. This was confirmed in the main study, where pulmonary resistance decreased from 2.6 (2.1-3.3) to 1.3 cm (0.8-2.2) HO/L/s after exercise (p = 0.006), whereas it remained unchanged after the turnout intervention. Following salbutamol administration after the turnout, lung function was comparable to that of the lunged horses, suggesting that the extent of exercise-induced bronchodilation was similar to that achieved with a β2-adrenergic agonist. MAIN LIMITATIONS: The small number of aged horses, the lack of blinding, and the focus on the short-term effects of exercise restrict the generalisability of the results. CONCLUSIONS: The rapid and potent bronchodilation achieved through brief aerobic exercise supports the investigation of a training program's impact on the management of SEA.