Executive Summary
 Exercise-induced pulmonary haemorrhage (EIPH) is a condition with high prevalence in racing thoroughbreds. However, despite its perceived importance as a cause of morbidity and impaired performance, few studies have attempted to address the relationship of EIPH to race performance.

Although many horsemen and veterinarians consider EIPH to be an important cause of poor performance, studies that have examined this relationship have not detected statistically significant relationships between EIPH and racing performance. Thus, the current study was conducted to investigate the association between performance and EIPH in a large number of thoroughbred race horses.

Endoscopic examinations were performed on 744 horses, representing 52.1% of those eligible horses starting during the study period. Both presence of EIPH and its severity were significantly (P < 0.05) associated with race performance. Horses with EIPH, defined as grade 2 or higher, were 4.0 times less likely to win, 1.8 times less likely to finish in the top 3 places, and finished 1.8 meters farther behind the winner than did unaffected horses. The severity of EIPH (grade 0-4) was significantly associated with reduced probability of winning, slower race time normalized to race length of 1200 meters, lower horse speed, and greater length behind the winner. Horses with grade 4 EIPH finished an average of 3.4 meters farther behind the winner than horses of grade 0.

These results demonstrate that EIPH has a significant negative relationship with race performance of thoroughbred horses. There is a proportional inverse relationship between severity of EIPH and performance. There was no evidence that EIPH was associated with superior performance. The results of this study therefore provide practitioners with valuable information regarding the effect of EIPH on performance of thoroughbred race horses that are not administered furosemide. Exerciseinduced pulmonary haemorrhage is a cause of reduced performance in thoroughbred race horses.