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.