Lung Function and Airway Cytologic Profiles in Horses with Recurrent Airway Obstruction Maintained in Low‐Dust Environments

Abstract

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 5 9), 2-3 years (time 2, n 5 7), and 5-6 years (time 3, n 5 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 5 .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 lowdust environments likely is due to irreversible airway remodeling but is not associated with cytologic evidence of airway inflammation.

Platelet-Activating Factor and Evidence of Oxidative Stress in the Bronchoalveolar Fluid of Thoroughbred Colts during Race Training

“…The alveolar macrophage function was investigated because of the inherent role of the alveolar macrophage in pulmonary defense. Our findings demonstrate that the EC resulted in increased phagocytosis as well as increased superoxide anion production, probably owing to increased aeroallergens and endotoxin in the horse stables 12,13,23,24 …”

“…Otherwise, the increased BALF nitrite observed in the EC group could be a response to environmental pollutants in the horse stables 12,13,23 . Furthermore, NO reacts with the superoxide anion (O − 2 ) to form the peroxynitrite (ONOO − ), a strong oxidant that can damage the pulmonary tissue resulting in lipid peroxidation 37 .…”

“…RAO is closely related to environmental factors, 12,13 but the contribution of the different environmental and stable factors, as etiological components of the airway inflammation of young athletic horses, awaits clarification 14 . In athletic horses, exercise and airway inflammation have long been associated, 2,3,15,16 and this association has also been reported for human athletes 17 …”

Investigating the Link between Particulate Exposure and Airway Inflammation in the Horse

“…Changes include increases in lung elastance, resistance, and transpulmonary pressures, and decreased dynamic lung compliance, with accompanying decline in arterial O 2 tension and increased arterial CO 2 tension . When dust exposure is minimized, RAO horses enter remission, with resolution of clinical and cytologic signs and improvement in lung resistance and transpulmonary pressure measurements …”

Markers of Systemic Inflammation in Horses with Heaves

“…Neutrophilic airway inflammation in horses with heaves can be reversed by antigen withdrawal. However, evidence suggests that the inflammatory processes are not completely shut down as residual peripheral airway bronchoconstriction, elevated smooth muscle cell turnover surrounding the airways, and higher nuclear factor κB (NF‐κB) activity are observable in asymptomatic horses with heaves. Although heaves is a disease of the airways, peripheral blood leukocyte activation and increased concentration of circulatory inflammatory mediators have been observed in affected horses during disease exacerbation suggesting that the inflammatory process might not be limited to the lungs.…”