Lung function and airway cytologic profiles in horses with recurrent airway obstruction maintained in low-dust environments

Background: The effects of long-term environmental management on airway obstruction and inflammation in horses with recurrent airway obstruction (RAO) are unknown. Hypothesis: Horses with RAO maintained in low-dust environments have persistent airway obstruction and neutrophilic inflammation. Animals: Study horses were treated for RAO and then maintained in low-dust environments with no medical management. Horses were classified into 3 groups by years after diagnosis: 1 year (time 1, n = 9), 2-3 years (time 2, n = 7), and 5-6 years (time 3, n = 8). The comparison groups were age-matched healthy horses. Methods: In this cross-sectional study, a clinical examination was performed, and the clinical score was calculated. Standard lung function, forced expiratory maneuvers, and the cytology of bronchoalveolar lavage fluid (BALF) were evaluated. Results: The clinical scores of the RAO horses were higher than those of the non-RAO horses at time 2 (P =.018). Standard lung function data were not different between the groups at any time point. The forced expiratory flow between 75-95% of exhaled vital capacity was lower in RAO horses than in non-RAO horses at all time points (P < .02), indicating persistent peripheral airway obstruction. Cytologic evaluation of BALF revealed no difference in total nucleated cell numbers or differential cell counts between RAO and non-RAO horses at any time point. Conclusions and Clinical Importance: The peripheral airway obstruction detected in horses with RAO maintained in low-dust environments likely is due to irreversible airway remodeling but is not associated with cytologic evidence of airway inflammation.