Risk factors for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses

Risk factors for occult exercise-induced pulmonary haemorrhage (EIPH) are poorly defined or quantified.

To investigate the importance of putative risk factors for EIPH amongst Thoroughbred racehorses in Australia.

Tracheobronchoscopy was used to determine EIPH status of 744 Thoroughbred racehorses after flat racing in Melbourne, Australia. Horses were identified for study before racing, and over 50% of horses racing during the study period were examined. Statistical analysis included use of bivariate and multivariate logistic regression analysis to account for simultaneous effects of a large number of variables.

The only risk factor identified as associated with both EIPH ≥ 1 or ≥ 2 was ambient temperature, with horses racing at temperatures <20 °C being at ∼ 2 times risk of occult EIPH. There was no association of EIPH with age, sex, weight carried, track hardness, speed of racing, or air quality.

There do not appear to be individual risk factors, amongst those examined in this study, that are strongly associated with EIPH.

The risk of developing EIPH cannot be readily determined from a combination of age, race speed, race distance, track hardness or air quality. This study does not provide support for the hypotheses that racing on hard surfaces or in polluted air contributes to the development of EIPH.