Comparison of respiratory secretion cytology and pulmonary histology in horses

Equine respiratory secretions (RS) collected before (33 horses) and after (76 horses) slaughter were evaluated cytologically and grouped according to the histological diagnosis of the lungs from which they were obtained. The histological categories included normal lungs (control; 17 horses), chronic small airway disease with mild (23 horses), moderate (13 horses) and severe lesions (25 horses), interstitial pneumonia (13 horses), pulmonary eosinophilic infiltration (13 horses) and pulmonary haemorrhage (5 horses). On a group basis there were significantly more neutrophils in RS of horses with mild, moderate and severe chronic small airway disease and interstitial pneumonia than in control horses. Horses with severe chronic small airway disease had significantly more lymphocytes and significantly fewer ciliated columnar epithelial cells in RS than control horses. Significantly more eosinophils were seen in RS of horses with pulmonary eosinophilic infiltration than in control horses. On an individual horse basis all horses with moderate and severe chronic small airway disease and with pulmonary haemorrhage had a RS cytology which differed from that of control horses; however, some horses with mild chronic small airway disease (11 horses), pulmonary eosinophilic infiltration (4 horses) and interstitial pneumonia (3 horses) did not have an RS cytology that differed from control horses.