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Exercise-induced pulmonary haemorrhage in Thoroughbred racehorses: an investigation of risk factors, the association with race day performance and a longitudinal study

Crispe, Eleanor (2018) Exercise-induced pulmonary haemorrhage in Thoroughbred racehorses: an investigation of risk factors, the association with race day performance and a longitudinal study. PhD thesis, Murdoch University.

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Exercise-induced pulmonary haemorrhage (EIPH) is a highly prevalent disease of racehorses. Recognised for centuries, there has been advances in our knowledge and understanding of the disease, but the cause and prevention of EIPH remains elusive. The aim of this study was to contribute to the knowledge base of EIPH with a broader exploration of risk factors, the impact of race day EIPH on a range of novel and routine performance parameters, and to document the longitudinal nature of the disease.

Subject to timing, tracheobronchoscopy after racing is a reliable technique to detect pulmonary haemorrhage. Although the association between tracheobronchoscopic haemorrhage and pulmonary histological changes has not been substantiated, the grading of tracheal haemorrhage is an accepted marker of disease presence and severity. A prospective, observational and longitudinal study design was used to examine a group of Thoroughbred racehorses competing in Western Australia. Horses were examined with tracheobronchoscopy between 30 and 220 minutes after racing. The examinations were reviewed and graded (0-4) by experienced veterinarians that were blinded to the horses’ identity, date of examination and performance. In total, there were 3,794 observations from 1,567 horses collected over a 3-year period.

Using a subset of animals, the association between EIPH and a variety of horse, race and climatic factors were examined. Racing at lower ambient temperature and horses’ racing with bar shoes were associated with EIPH presence and increasing severity. Increasing race distance was associated with EIPH being detected and increasing the number of career race starts increased the risk of more severe EIPH.

Using the entire dataset horses with the most severe grades of EIPH (≥3) were significantly more likely to have a lower finishing position and finish further behind the winner, less likely to place in the first 3 positions and collect race earnings, collected less earnings per race start and were slower over the last 600m of the race than horses without EIPH (grade 0). Mild or moderate haemorrhage was not associated with inferior race day performance.

The longitudinal analysis of disease progression was conducted using 747 horses with a minimum of 2 observations. Tracheobronchoscopic EIPH mildly increased in severity over the first thirty race starts. The preceding EIPH score was significantly associated with the current EIPH score. Significant factors associated with the current EIPH score included ambient temperature and the number of days in the current racing preparation. Ambient temperature, weight carried in races and the number of days since last racing was associated with variation in EIPH severity between races.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Lester, Guy and Secombe, Cristy
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