Bar shoes and ambient temperature are risk factors for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses

Reasons for performing study: Ambient temperature has been identified as a risk factor for exercise-induced pulmonary haemorrhage (EIPH) in racing Thoroughbreds. This warranted a more expansive investigation of climatic conditions on the incidence and severity of EIPH. The impact of other variables such as the type of bit used, tongue ties and nonstandard shoes has not been reported and also warrant investigation. Objectives: To examine the effect of various climatic variables as contributing risk factors for EIPH. Other previously uninvestigated variables as well as standard track and population factors will also be examined. Study design: Cross-sectional study. Methods: Thoroughbred racehorses competing at metropolitan racetracks in Perth, Western Australia were examined 30-200 min post race with tracheobronchoscopy. Examination took place at 48 race meetings over a 12 month period. Examinations were graded (0-4), independently by two experienced veterinarians. Univariable analyses were performed and variables with a P<0.25 were entered into a multivariable logistic regression analysis. The analysis was performed twice using the presence of blood (EIPH grade 0 vs. grades >= 1) and EIPH grades <= 1 vs. EIPH grades >= 2 as dependent variables. Results: Exercise-induced pulmonary haemorrhage was diagnosed in 56.6% of observations. Lower ambient temperature was significantly associated with EIPH grades >= 1 (OR 0.95; 95% CI 0.93-0.98) and EIPH grades >= 2 (OR 0.97; 95% CI 0.94-1.0). Bar shoes were significantly associated with EIPH grades >= 1 (OR 6.35; 95% CI 2.17-18.54) and EIPH grades >= 2 (OR 2.72; 95% CI 1.3-5.68). Increasing race distance was significantly associated with EIPH grade >= 1 and increasing lifetime starts was significantly associated with EIPH grade >= 2. Conclusions: Ambient temperature is a risk factor for EIPH in Thoroughbred racehorses, with lower temperatures associated with increased risk. Bar shoes are a novel risk factor for EIPH in this population.