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Study Shows How Respiratory Disorder Slows Some Racehorses

September 15, 2005
Ohio State University
A respiratory disorder that causes thoroughbred racehorses to hemorrhage during competition may seriously hamper some horses' chances of winning a race. 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.
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A new study inAustralia found that horses with more severe forms of this disorder,called exercise-induced pulmonary hemorrhage (EIPH) trailed the winnerby an average of 14 feet (4.36 meters). EIPH causes blood to leak fromthe pulmonary artery into the bronchial tubes and windpipe duringintense exercise, making it harder for an animal to breathe.

Thephysical stress of racing triggers EIPH in about half of allthoroughbreds, said Kenneth Hinchcliff, the study's lead author and aprofessor of veterinary clinical sciences at Ohio State University.

“Thedisorder is clearly an important cause of poor performance in racehorses,” he said. “The thoroughbred racing community long suspectedthat EIPH hindered race performance, yet there wasn't any scientificevidence to link the two.

“This is the first study to demonstrate that connection.”

Thedisorder affects about half of all racehorses in North America, buthorses here are often given a diuretic, called furosemide (brand nameSalix), in an attempt to prevent EIPH. Furosemide is banned by racingcommissions in many other countries.

EIPH is graded on a scale ofzero to four, with four being the most severe form. In this study, 55percent of the 744 horses examined after a race had developed EIPH tosome degree. The horses with an EIPH grade of one or lower were just aslikely to win a race or come in second or third as were horses withouta trace of blood in their airways. But the odds of winning or placingsecond or third were markedly worse for horses with an EIPH of gradetwo or higher.

The findings appear in a recent issue of the Journal of the American Veterinary Medical Association.

Hinchcliffconducted the study while on sabbatical in Australia , where thethoroughbred racing industry prohibits trainers from giving theircompetitive animals furosemide. More than 90 percent of North Americanracehorses are given the drug before competing. About six years ago,Hinchcliff and Paul Morley, of Colorado State University and aco-investigator on the current research, found that the drug seemed toimprove performance on North American racetracks.

“Manyracehorses in the U.S. get furosemide before a race, but we don'tactually know if it works that well for preventing EIPH,” Hinchcliffsaid.

In the current study, the researchers collected data on 744thoroughbreds that ran in races at one of four courses in Melbourne .The horses competed in 202 races at 26 meets. Animals were enrolled inthe study one to two days before a race. After each race, Hinchcliffand his colleagues examined each horse by inserting an endoscope intoone of animal's nostrils and then through its throat and into thewindpipe.

An EIPH grade of four means that more than 90 percentof the horse's windpipe is covered in blood. An EIPH grade of oneindicates that a few flecks or tiny streams of blood were spotted ineither the windpipe or the bronchial tubes. A grade of zero means thata horse is EIPH-free.

Of the 412 horses in this study thatdeveloped EIPH, most (273) had a grade of one or less. These animalsperformed just as well as those without any trace of blood in theirairways. They were four times as likely to win a race and nearly twice(1.8 times) as likely to finish in one of the top three positions aswere horses with an EIPH of grade two, three or four.

Forracehorse trainers and owners, the presence of EIPH can have financialimplications, too. Horses with grade one EIPH were three times morelikely to win take-home earnings than were animals with EIPH of gradetwo or higher.

Of the remaining 139 horses with the disorder, 101were diagnosed with grade two; 25 had grade three; and 13 horses hadgrade four EIPH. The more severe the disorder, the further behind thewinner a horse was likely to place.

“We could actually quantifythe distance based on the severity of the disorder,” Hinchcliff said.“If a horse was a grade three or grade four bleeder, that was one tosix meters (about three to 19 feet) in race distance.”

Hinchcliffalso pointed out that it doesn't matter how old a horse is or how longit has raced – any thoroughbred racer could develop some degree ofEIPH. He and his colleagues also aren't sure if the disorder getsprogressively worse in a horse that develops a less severe grade.

Whilemost racehorses in North America are given a drug prior to racing in anattempt to prevent hemorrhaging, EIPH is still tough to control.Hinchcliff said that there are a number of treatments that are used,including herbal products, but whether or not these act as trulyeffective remedies isn't clear.

Hinchcliff is co-investigator ona current study being conducted in South Africa , where furosemide isalso banned, to see if the results are similar to those of theAustralian study.

Hinchcliff conducted the current study withresearchers from the School of Veterinary Science at the University ofMelbourne; Racing Victoria, Ltd., in Flemington, Victoria, Australia;and from the college of veterinary medicine at Colorado StateUniversity in Fort Collins.

Funding was provided by Racing Victoria Limited and Rural Industries Research and Development Corporation, Australia .

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The above story is based on materials provided by Ohio State University. Note: Materials may be edited for content and length.

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Ohio State University. "Study Shows How Respiratory Disorder Slows Some Racehorses." ScienceDaily. ScienceDaily, 15 September 2005. <>.
Ohio State University. (2005, September 15). Study Shows How Respiratory Disorder Slows Some Racehorses. ScienceDaily. Retrieved April 25, 2015 from
Ohio State University. "Study Shows How Respiratory Disorder Slows Some Racehorses." ScienceDaily. (accessed April 25, 2015).

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