Prevalence of exercise-induced pulmonary hemorrhage in competing endurance horses

To assess the prevalence of exercise-induced pulmonary hemorrhage (EIPH) among elite endurance horses after competition in a long-distance race.

20 endurance horses and 12 nonexercised or minimally exercised age-, breed-, and trainer-matched horses from the same environment (control horses).

Bronchoalveolar lavage fluid samples collected from endurance horses at 3 to 8 days (sample A) and 36 to 38 days (sample B) after the race (100 km in 1 day [n = 3], 70 km/d for 2 days [12], or 100 km/d for 2 days [5]) were cytologically examined for the presence of hemosiderophages. Samples from control horses were collected at the same time as sample B was obtained from respective matched endurance horses and similarly examined. Horses with bronchoalveolar lavage fluid samples in which > 1% of identified cells were hemosiderophages were considered to have evidence of EIPH.

Of 20 endurance horses, 9 (45%; 95% confidence interval, 25% to 66%) and 10 (50%; 95% confidence interval, 29% to 71%) had cytologic evidence of EIPH in samples A and B, respectively. Evidence of EIPH was present in 6 of 20 (30%) horses at both sample collection times, 3 (15%) at the first sample time only, and 4 (20%) at the second sample time only. In contrast, 1 of 12 control horses had cytologic evidence of EIPH.

The prevalence of EIPH in these elite endurance horses (45% to 50%) was higher than previously reported estimates for poor-performing endurance horses; however, differences in criteria for identification of EIPH should be considered when comparing findings between studies.