WSU to study effect of controversial drug on racehorses

Horses race in a derby.
Overall, the WSU team plans to analyze information gathered from about 30,000 racehorses for the study (photo by Philippe Oursel courtesy of Unsplash).

Washington State University researchers have been awarded more than $370,000 for a two-year study into the impact of a controversial drug administered to thoroughbred racehorses before most races in the United States to reduce bleeding in the animals’ lungs.

The drug in question, furosemide, a diuretic commonly known as Lasix, has been shown to reduce the prevalence and severity of exercise-induced pulmonary hemorrhage (EIPH) — a condition that causes bleeding in the lungs during exercise. Detractors, however, question its true effectiveness, contending it leads to other health ramifications while also creating public perception issues for the sport. Most major racing jurisdictions internationally prohibit race-day use of the drug, and a permanent ban is under consideration in the U.S.

“We hypothesize that our study will show horses that regularly get furosemide before racing have more races and longer careers than those that don’t,” said Dr. Warwick Bayly, who is leading the research alongside fellow professor Dr. Macarena Sanz in the WSU College of Veterinary Medicine. “The results of this study are going to help guide the final decision on the future use of furosemide.”

The grant was awarded by the Horseracing Integrity and Safety Authority, a private self-regulatory organization created by Congress in 2020 to regulate thoroughbred racing in the U.S. HISA has essentially banned the use of furosemide, although most tracks applied for and received a waiver while studies into the drug are conducted. Even with the waivers, most major racetracks have banned race-day use of furosemide in stakes races, like the Kentucky Derby, and in horses younger than 3 years old.

HISA is expected to make a final decision on the use of furosemide in 2026 based on the findings of this study and others it has funded examining the effects of the drug.

Overall, the WSU team plans to analyze information gathered from about 30,000 racehorses for the study.

The work will begin with analyzing the career trajectories of racehorses that began competing in 2011, tracking their performances until 2019. This phase seeks to determine if regular furosemide treatment correlates with increased career longevity and race participation.

The team will also investigate the impact of banning furosemide on the careers and number of starts for 2-year-old racehorses. Horses that raced before the ban, between 2015 and 2019, will be compared to those that raced post ban, from 2021 to 2025.

“There are many things that result in a horse ending its career, and there are a lot of things that determine how many races it would have,” Bayly said. “Our theory is that one of those determinants is the severity of the EIPH. A couple of really clever statisticians are participating in the study, and we have to sift through all this data and try and work out whether or not the frequency of Lasix administration is related to career duration.”

Researchers will also use data collected from videos of racehorses scoped at racetracks in early 2024 to evaluate the severity of EIPH and its influence on race participation over the subsequent 18-month period. Collectively, the results of the three studies should provide vital information that will help inform future HISA regulations on the pre-race use of furosemide in thoroughbreds.

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