A new study in Australia found that horses with more severe forms of this disorder, called exercise-induced pulmonary hemorrhage (EIPH) trailed the winner by an average of 14 feet (4.36 meters). EIPH causes blood to leak from the pulmonary artery into the bronchial tubes and windpipe during intense exercise, making it harder for an animal to breathe.
The physical stress of racing triggers EIPH in about half of all thoroughbreds, said Kenneth Hinchcliff, the study's lead author and a professor of veterinary clinical sciences at Ohio State University.
"The disorder is clearly an important cause of poor performance in race horses," he said. "The thoroughbred racing community long suspected that EIPH hindered race performance, yet there wasn't any scientific evidence to link the two.
"This is the first study to demonstrate that connection."
The disorder affects about half of all racehorses in North America, but horses here are often given a diuretic, called furosemide (brand name Salix), in an attempt to prevent EIPH. Furosemide is banned by racing commissions in many other countries.
EIPH is graded on a scale of zero to four, with four being the most severe form. In this study, 55 percent of the 744 horses examined after a race had developed EIPH to some degree. The horses with an EIPH grade of one or lower were just as likely to win a race or come in second or third as were horses without a trace of blood in their airways. But the odds of winning or placing second or third were markedly worse for horses with an EIPH of grade two or higher.
The findings appear in a recent issue of the Journal of the American Veterinary Medical Association.