Association Between Race Time and Furosemide Administration in Standardbred Race Horses

Although the size of the effect varies with sex of the horse, administration of furosemide to Standardbred race horses is associated with faster race times. However, when horses are administered furosemide for the first time, an association between furosemide and faster race times is not apparent.

1. Introduction

Furosemide is administered to large numbers of Thoroughbred and Standardbred racehorses as a prophylaxis for exercise-induced pulmonary hemorrhage. Thoroughbred racehorses that are administered furosemide have superior performance evidenced by faster 6-furlong race times, higher probabilities of winning, and greater earnings [1]. Similarly, of 788 Standardbred pacers racing at one track in Pennsylvania, those administered furosemide had faster race times than did untreated horses [2]. The purpose of the current study was to determine if this association was present in a larger sample of both trotters and pacers racing at tracks throughout the United States. Furthermore, we examined whether there was a °first-time° effect of furosemide administration on race time.

2. Materials and Methods

Performance records used in this study were obtained from the United States Trotting Association (USTA) for all Standardbred horses racing in USTA-sanctioned 1-mi races in the United States between June 27, 1998 and July 11, 1998. Only the first sanctioned competitive performances for each horse during that time period was included; official timed workouts were excluded. Horses were excluded from the study if they did not finish the race or if information was not available regarding the winning race time, individual performance time, post position, whether the horse broke stride, or whether the horse was interfered with or impeded during the race. Data were summarized, and descriptive statistics were calculated. Data were analyzed using principal components in analysis of variance and logistical regression as previously described [1]. Furosemide administration (yes or no) was the primary independent variable of interest and was included in all multivariable analyses. In addition, all available variables that were thought to have possibly affected or predicted the quality of the horses’ performance were controlled in analyses.

3. Results

Race records for 20,720 horses racing at 82 tracks were included in the analysis. Furosemide was administered to 4631 horses (22.35%) of which 97 received furosemide for the first time. There was a significant association between furosemide administration and sex with 16.2% of females and 26.0% of males being medicated. Similarly, there was a significant association between age and proportion of horses administered furosemide with the proportion of horses receiving furosemide increasing with age. Univariate analysis revealed a significant association between furosemide administration and winning, placing in the top three positions, and earning money. Multivariate analysis using principal components showed a significant relationship between furosemide administration and race time that varied with sex. Females administered furosemide finished 0.18 s faster than untreated females, treated geldings finished 0.05 s faster than untreated geldings, and treated stallions finished 0.11 s faster than did untreated stallions. Horses administered furosemide for the first time did not have faster race times than did untreated horses.

4. Discussion

This study provides further evidence of an association between furosemide administration and athletic performance in Standardbred race horses. The study results are widely applicable because of the large number of horses examined at a wide range of tracks. The mechanism underlying superior performance by furosemide-treated horses is unknown, although weight loss or an effect on severity of exercise-induced pulmonary hemorrhage are potential explanations. The fact that horses treated with furosemide for the first time did not have superior performance compared with untreated horses suggests that, in Standardbreds, the effect of furosemide on performance may not be related to weight loss.

The authors gratefully acknowledge the assistance of the United States Trotting Association in providing race records.