Study shows how respiratory disorder slows some racehorses

09/14/05

COLUMBUS , Ohio – 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.

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.

Hinchcliff conducted the study while on sabbatical in Australia , where the thoroughbred racing industry prohibits trainers from giving their competitive animals furosemide. More than 90 percent of North American racehorses are given the drug before competing. About six years ago, Hinchcliff and Paul Morley, of Colorado State University and a co-investigator on the current research, found that the drug seemed to improve performance on North American racetracks.

"Many racehorses in the U.S. get furosemide before a race, but we don't actually know if it works that well for preventing EIPH," Hinchcliff said.

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

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

Of the 412 horses in this study that developed EIPH, most (273) had a grade of one or less. These animals performed just as well as those without any trace of blood in their airways. 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 as were horses with an EIPH of grade two, three or four.

For racehorse trainers and owners, the presence of EIPH can have financial implications, too. Horses with grade one EIPH were three times more likely to win take-home earnings than were animals with EIPH of grade two or higher.

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

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

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

While most racehorses in North America are given a drug prior to racing in an attempt 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 truly effective remedies isn't clear.

Hinchcliff is co-investigator on a current study being conducted in South Africa , where furosemide is also banned, to see if the results are similar to those of the Australian study.

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

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

Source: Eurekalert & others

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