Assessment of the exercise tests used during overground endoscopy in UK thoroughbred racehorses and how these may affect the diagnosis of dynamic upper respiratory tract obstructions

Reasons for performing study: Overground endoscopy is being performed with increasing frequency in the UK. A previous study has shown that the type of exercise test may affect the diagnosis of upper respiratory tract (URT) obstructions. The successful clinical application of overground endoscopy systems requires understanding of appropriate field exercise testing protocols. Objectives: The aim of this study was to report the exercise test parameters used during overground endoscopy in UK Thoroughbred racehorses and to investigate potential effects of these on the diagnosis of URT obstructions. Methods: The exercise test parameters used and the endoscopic observations of the URT during exercise were recorded for 140 Thoroughbred racehorses referred for the investigation of abnormal respiratory noise and/or poor athletic performance. Results: The exercise test parameters varied widely between horses. The presenting complaint was easiest to reproduce in horses with a history of abnormal noise in training and hardest to reproduce in those referred for investigation of poor performance with no abnormal noise. No associations between the presence or not of an URT obstruction and exercise test parameters was identified. For horses referred for abnormal noise during racing DDSP was more likely to be observed when longer distances were performed. Conclusions: It is difficult to standardise exercise tests in the field when multiple premises are used and when training gallops differ markedly to racecourses. It was not possible to establish exercise test protocols which should be used for all Thoroughbred racehorses. Therefore, at present the best advice for horses whichmake abnormal noise during a race or have poor race performance, can only be to replicate race conditions as closely as possible. For horses that race over longer distances this will require the use of a circular gallops (e.g. racecourse) if only short gallops are available at the trainer’s premises.