The association between exercise-induced pulmonary haemorrhage and race-day performance in Thoroughbred racehorses

Exercise-induced pulmonary haemorrhage (EIPH) is commonly implicated as a cause of poor athletic performance but there is limited and conflicting evidence for this association.

The aim of this study was to determine if EIPH, based on endoscopic examination after racing, is associated with a variety of novel and established performance parameters.

Prospective, observational cross-sectional study.

Thoroughbred racehorses competing between 2012 and 2015 were examined on-course no earlier than 30 min after racing. Examinations were recorded and graded blindly by experienced veterinarians using a 0-4 scale. Linear mixed effect models were used for analysis of continuous response variables with horse name incorporated as a random effect to account for repeated sampling and horse variability. Generalised estimating equations were used for analysis of binary responses. Performance variables were examined in 2 models, comparing EIPH grade 0 to grades 1-4, and EIPH grade ≤2 compared with EIPH grades ≥3, controlling race factors that could influence performance.

There were 3794 observations collected from 1567 horses. EIPH was detected in 55.1% of observations. Horses with grade 4 EIPH 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 600 m of the race than horses without EIPH (grade 0). Similar associations were seen in Model 2, with horses with EIPH grade ≥3 having inferior performance when compared to horses with EIPH ≤2.

Enrolment was voluntary.

Mild to moderate haemorrhage was not associated with inferior race day performance in this population of Thoroughbred racehorses.