Mild, Moderate EIPH Not Associated With Race Performance

Mild, Moderate EIPH Not Associated With Race Performance

A study of nearly 1,600 Thoroughbreds showed no significant differences in racing results between horses with Grades 1, 2, or 3 EIPH and unaffected horses.

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A racehorse with severe lung bleeding might not run as well as his unaffected competitors. But a slight case of exercise-induced pulmonary hemorrhage (EIPH) doesn’t seem to impact a horse’s placing at the finish line, Australian researchers say.

A study of nearly 1,600 Thoroughbreds racing in Australia between from 2012 through 2015 showed no significant differences in racing results between horses with Grades 1, 2, or 3 EIPH (mild to moderate bleeding) and unaffected horses, said Guy Lester, BVMS, PhD, Dipl. ACVIM, of the Murdoch University College of Veterinary Medicine in the School of Veterinary and Life Sciences, in Western Australia. The study horses had not been treated with furosemide (commonly called Lasix or Salix), a drug used to reduce EIPH severity, before racing.

However, the researchers noted that horses with Grade 4 EIPH (more severe bleeding) were significantly more likely to finish in a lower placing and cross the finish line more lengths behind the winner compared to horses without EIPH, Lester said. They also tended to be less likely to place in the first three positions or collect race earnings. And if they did collect earnings, these were relatively lower per start. Another interesting finding, he added, was that they tended to slow down in the final stretch of the race.

“Bad bleeders (in our study) tended to be faster than other horses in the early to middle stages of the race, but then slower in the last 600 meters,” Lester said.

However, while there’s clearly an association between severe hemorrhaging and reduced performance, the cause-and-effect relationship remains undetermined. “Is this because they experience EIPH?” Lester said. “Or do they simply fatigue from overexertion in the early phases of the race? I’m not certain we fully understand this yet.”

Their study showed that about 55% of the horses had some grade of EIPH—which is consistent with previous study results, he said. However, this is neither surprising nor particularly alarming, he added.

“We breed animals to maximize performance, and a byproduct of this is a very thin membrane between the pulmonary blood vessel and the alveolus (the small air sacs comprising the innermost structure of the lungs), allowing for highly efficient uptake of oxygen and loss of carbon dioxide,” Lester said. “I think EIPH is an expected condition in elite equine athletes (across a range of disciplines) performing at maximal levels of exertion.”

And EIPH isn’t just an equine phenomenon, he added. It also affects other species, including humans. “The famous respiratory physiologist John West (MD, PhD, DSc, emeritus professor at the University of California, San Diego, Department of Medicine Division of Physiology) once stated that EIPH may be an evolutionary consequence to athletic elitism,” he said.

Why it’s associated with reduced performance in severe grades, however, is still somewhat of a mystery, Lester said. “The specific basis is unknown, but a prevailing opinion is that failure of the pulmonary capillaries and hemorrhage into the airways impairs the critical gas exchange necessary for maximal performance,” he said.

“The magnitude of the bleeding may be proportionate to declines in gas exchange,” Lester continued. “There are also factors that are difficult to evaluate, such as whether horses experience a sense of ‘concern’ when they experience a particularly large bleed. Some have suggested that horses could equate racing with a negative experience and therefore may reduce effort in subsequent races.”

For now, however, researchers just don’t know.

Lester’s group is currently studying the consistency of EIPH in individual horses, finding that “bleeders” don’t always bleed, or not at the same grade, every race, he said. Check for updates.

The study, “The association between exercise-induced pulmonary haemorrhage and race-day performance in Thoroughbred racehorses,” was published in the Equine Veterinary Journal

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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