Decreases in energy generation during exercise found in furosemide-treated horses were attributed to the losses in body weight caused by the drug's diuretic action.
One of the most controversial issues in horse racing is the debate over the use of the loop diuretic furosemide (also known as Salix or Lasix) in the prevention of exercise-induced pulmonary hemorrhage (EIPH), a condition characterized by bleeding into the lungs during intense exercise. It has long been known that furosemide administration improves horses' racing performance when compared to non-medicated horses. Researchers at the University of Kentucky conducted a study to measure the effects of furosemide on horses' energy efficiency during a standardized exercise test (SET).
Six Thoroughbred geldings with an average age of 6.8 years were selected for the study. For 21 days leading up to the SET, all horses received 13 pounds of hay, 9 pounds of grain, and 0.5 pounds of a vitamin/mineral supplement. Horses were not given access to water or feed for the 4 hours leading up to the SET. All horses were weighed 4 hours before the SET, immediately before and after the SET, as well as at 4, 8, 12, 24, 48, and 72 hours after the SET. Heart rate, VO2, and VCO2 were measured at intervals throughout the SET. Blood samples were also taken before, after, and during the SET to measure lactate, glucose, total protein (TP) concentrations, and packed cell volume (PCV). One hour following the SET, all horses were assessed and graded for EIPH by tracheobronchial endoscopy.
In this study, horses treated with furosemide prior to the SET experienced significantly greater weight loss (27 pounds, compared to 12 pounds in untreated horses). Untreated horses had higher heart rates during the SET and greater lactate accumulation, indicating more energy expenditure. Weight-adjusted VO2 and VCO2 measurements did not differ significantly between treated and untreated horses. EIPH incidence after the SET was low and not associated with treatment.
Rather than reduced EIPH, decreases in energy generation during exercise found in the furosemide-treated horses in this study were attributed to the losses in body weight caused by the drug's diuretic action.
Summarized by Sam Beeson, Univ. of Minn. Veterinary Student