Lasix Reduces Bleeding in Horses’ Lungs, Study Says

The debate about whether thoroughbreds should be treated with a diuretic on the day of a race became thornier Monday when researchers released a study showing that furosemide, known as Lasix, significantly reduces bleeding in horses’ lungs.

Furosemide has been used to treat racehorses since the 1970s. Most countries ban race-day use of Lasix because it improves performance. In the United States, however, virtually every horse receives it on the day of the race.

“The results of this study do not eliminate debate about the use of this medication in racehorses, but it does provide evidence needed to aid making sound policy decisions,” Dr. Paul Morley, one of the principal investigators of the study and a veterinarian at Colorado State University, said in a telephone interview. The study will appear in The Journal of the American Veterinary Medical Association.

Thoroughbreds running at racing speeds experience varying degrees of exercise-induced pulmonary hemorrhage, or bleeding in their lungs. While severe bleeding is uncommon — about 2 percent of racehorses are sidelined because of the malady — the study confirmed what American horsemen had argued but that no data supported: bleeding impaired horses’ performances.

“We know that furosemide is associated with improved performance, and that exercise-induced pulmonary hemorrhage markedly affects race performance,” Dr. Kenneth W. Hinchcliff said in a telephone interview. “But we didn’t know the answer to the third — and most important — leg of the trifecta: whether furosemide is effective in treating E.I.P.H. We now know.”

The study was conducted on 167 racehorses in South Africa in 2007 by an international team of veterinarians: Morley, of Colorado State; Hinchcliff, of the University of Melbourne in Australia; and Dr. Alan J. Guthrie of the University of Pretoria in South Africa. Each horse in the study raced twice, once after receiving Lasix before the race and once after receiving a placebo.

Results showed that horses were 3 to 11 times as likely to suffer some bleeding while running on the placebo as they were after receiving the Lasix. About two-thirds of the horses that had some bleeding under the placebo had a reduction in its severity when treated with Lasix, the study said.

It also demonstrated how, beyond the prospect of unobstructed breathing, the medication can enhance the performance of a horse. Horses that were treated with Lasix lost an average of 27.9 pounds between injection and a weight measurement after the race, while untreated horses lost an average of 11.9 pounds.