New Published Study on EIPH and Thoroughbred Racehorses

Editor’s Note: Jeff Dodge, a freelance writer for Colorado State University, was the author of the following press release. Below is information provided by EquiManagement from the latest research study mentioned in this press release.

As the debate over the controversial drug Lasix heats up in advance of the Breeders’ Cup this week, a Colorado State University researcher has released new study results about the impact that bleeding in the lungs has on racehorses’ performance and the effectiveness of the most common treatment for the condition.

Lasix, the original brand name for a diuretic called furosemide, is used by horse owners to reduce exercise-induced pulmonary hemorrhaging (EIPH), the bleeding in the lungs that commonly occurs while horses are racing.

The use of the medication was banned by the Breeders’ Cup last year in races that were limited to 2-year-old horses, but race officials reversed that policy and are allowing Lasix to be used in all races this year. The industry in North America is divided over the issue, with proponents of the diuretic arguing that Lasix protects horses’ health and improves performance, and opponents saying that permitting the drug is marring the sport’s good name.

The Breeders’ Cup, a 30-year-old series of Thoroughbred races, will be held Oct. 31-Nov. 1 at Santa Anita Park in Arcadia, California.

Recent research by Paul Morley, DVM, PhD, DACVIM, a CSU professor in the Department of Clinical Sciences and one of the foremost experts on Lasix and EIPH, is providing important new information to stakeholders in the debate. Morley is part of a long-standing collaborative group that has published three new papers in Equine Veterinary Journal that address the effects of EIPH on performance as well as the efficacy of Lasix in controlling the condition.

In the first study, Morley and his co-authors studied EIPH in 1,000 racehorses, and showed that the condition has detrimental effects on their ability to perform as elite athletes. However, in another study that followed the lifetime racing careers of more than 700 horses, the research group was unable to find an association between EIPH and the number of races the horses were able to run or their earning potential, except in the most extreme form of the condition. In the third project, Morley and his research team examined existing studies on Lasix and concluded that there is high-quality, albeit limited, evidence that Lasix is effective in reducing the incidence and severity of EIPH in racehorses. The finding supports the results of his team’s landmark 2009 clinical trial on Lasix.

“Dr. Morley is very highly regarded worldwide,” said Dr. Thomas Tobin of the Gluck Equine Research Center at the University of Kentucky. “Everything he does carries significant weight because of the longtime recognition of his research and the quality of his work.”

“These studies build on our earlier work to provide horsemen and regulators with the evidence they need to inform the highly charged debate about EIPH and Lasix,” added Ken Hinchcliff, dean of the faculty of Veterinary and Agricultural Sciences at the University of Melbourne, Australia, and one of Morley’s longtime collaborators on the studies. “Our international team has explicitly addressed the key issues facing racing around the management of EIPH.”

Despite the controversy surrounding the issue, Morley said he and his fellow researchers don’t have a horse in the race, so to speak; they are simply trying to provide independent, unbiased information so that ongoing discussions about Lasix are based on sound facts.

Morley acknowledged that there is much more research to be done, since the long-term effects of EIPH and Lasix on the wellbeing of horses are still unclear.

“We want to continue providing high-quality evidence for the decision-makers, to inform the debate,” he said.


Editor’s Note: An article has been accepted for publication in the Equine Veterinary Journal entitled “Exercise-induced pulmonary haemorrhage impairs racing performance in Thoroughbred racehorses.” The article is available in pre-publication form on Following is the abstract of this paper.


Reasons for Performing Study

Exercise-induced pulmonary haemorrhage (EIPH) occurs commonly in Thoroughbred racehorses worldwide. While EIPH is believed to be an important cause of impaired performance in these horses, there is limited evidence from sufficiently powered studies to evaluate this association.


To evaluate whether EIPH is associated with finishing position, distance finished behind race winners, and differences in race earning among Thoroughbred horses racing in South Africa.

Study Design

Prospective cross-sectional study.


1,000 Thoroughbred horses racing in South Africa were enrolled prior to a single race and underwent tracheobronchoscopic examination within 2 hours of racing. Three observers, blinded to the horses’ identity and race performance, independently evaluated EIPH occurrence and severity using video recordings of the examination. Data were analysed using multivariable logistic and linear regression while controlling for important horse and race factors as potential confounding variables.


Overall, 68% of horses had evidence of EIPH (grade ≥1). Horses without evidence of EIPH (severity grade 0), when compared to horses with any evidence of EIPH (grade ≥1), were >2 times more likely to win races (OR = 2.3; 95%CI=1.4–3.7; P = 0.001), finished an average of one length ahead of horses with EIPH (P = 0.03), and were 2.5 times more likely to be in the highest decile in race earnings (OR = 2.5, 95%CI = 1.5-4.1, P<0.001). However, no association was identified regarding finishing in the top 3 positions or earning money when analysed as a continuous variable or analysed as any winnings vs. none.

EIPH was associated with impaired performance in Thoroughbred racehorses not medicated with furosemide and not using nasal dilator strips. These findings provide strong corroboration of previous research indicating that the occurrence of EIPH has a major impact on the ability of Thoroughbred racehorses to compete successfully as elite athletes.


P. S. Morley, and J. L. Bromberek, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University; M. N. Saulez, Equine Research Center, Faculty of Veterinary Medicine, University of Pretoria, Onderstepoort, South Africa and Drakenstein Veterinary Clinic, Western Cape, South Africa (This work formed part of Dr. Saulez’s PhD studies.); K. W. Hinchcliff, Equine Research Center, Faculty of Veterinary Medicine, University of Pretoria, Onderstepoort, South Africa; and A. J. Guthrie, Faculty of Veterinary Medicine, University of Melbourne, Werribee, Victoria, Australia.

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