Effect of different protocols on the mitigation of exercise-induced pulmonary hemorrhage in horses when administered 24 hours before strenuous exercise

Background: Public pressure exists in the United States to eliminate race-day furosemide administration despite its efficacy in decreasing the severity of equine exercise pulmonary hemorrhage (EIPH). No effective alternative prophylaxis strategies have been identified.

Objective: To investigate alternative protocols to race-day furosemide that might mitigate EIPH.

Animals: Seven fit Thoroughbreds with recent EIPH.

Methods: Double-blinded placebo-controlled Latin square crossover using a treadmill followed by a blinded placebo-controlled crossover study at a racetrack. First, horses exercised supramaximally to fatigue 24 hours after initiating 5 EIPH prophylaxis protocols: 0.5 and 1.0 mg/kg furosemide IV 24 hours pre-exercise with and without controlled access to water, and 24 hour controlled access to water. Effects were compared to those measured after giving a placebo 24 hours pre-exercise, and 0.5 mg/kg furosemide IV 4 hours pre-exercise. Bronchoalveolar lavage (BAL) erythrocyte count was determined 45-60 minutes postexercise after endoscopy to assign an EIPH score. Data were analyzed using linear mixed effects models. The most promising protocol from the treadmill study was further evaluated in 6 horses using endoscopy and BAL after 1100 m simulated races.

Results: Intravenous furosemide (0.5 mg/kg) administered 24 hours pre-exercise combined with controlled access to water decreased the severity of EIPH on the treadmill and at the racetrack.

Conclusion and clinical importance: Administering 0.5 mg/kg furosemide 24 hours pre-racing combined with controlling water intake may be a strategy to replace race-day furosemide administration for the management of EIPH. A larger study is indicated to further evaluate whether this protocol significantly mitigates EIPH severity.