Physiological measurements and upper and lower respiratory tract evaluation in French Standardbred Trotters during a standardised exercise test on the treadmill.

Abstract

There are a variety of reasons for poor performance in racehorses. Exercise intolerance has often been associated with subclinical respiratory abnormalities, and diagnostic aids are therefore used to enhance clinical detection. Physiological variables can also be measured in order to evaluate the metabolic reponse to exercise. This study evaluated the relationship between physiological measurements and upper airway videoendoscopy during a standardised treadmill exercise test and bronchoalveolar lavage (BAL) cytology in control horses (good racing performance, n = 14) and poor performers (n = 27). The poor performers were divided into 2 groups: Group 1 = both upper and lower respiratory airway abnormal findings (n = 10); Group 2 = lower respiratory airway abnormal findings (n = 17). Horses in Group 2 were divided into 3 categories: Group 2A = exercise-induced pulmonary haemorrhage (EIPH ; n = 5); Group 2B = small airway inflammation (SAI +/- EIPH; n = 7) and Group 2C = other (n = 5). During exercise, the poor performers had significantly lower arterial PaO2 and higher HR and blood lactate concentrations compared to controls. Total nucleated cell count of BAL fluid collected from poor racing performers was significantly higher than in controls; also, epithelial cells and haemosiderophage percentage collected from poor racing performers were significantly higher than in controls. Eight horses with dorsal displacement of the soft palate also had cytological evidence of lower respiratory airway disease. The results of this study suggest that there is a significantly different metabolic response (HR, blood lactate, PaO2) to exercise in poor compared to good performers. As both upper and/or lower respiratory problems can be associated with poor racing performance, a detailed examination of the upper and lower respiratory tracts at rest, during and after exercise is advised.