Subclinical leptospirosis may impair athletic performance in racing horses.

The infection by Leptospira in horses, in both its acute disease and subclinical forms, is very common, particularly in endemic regions. Therefore, the objective of this study was to evaluate the effects of subclinical leptospirosis in the athletic performance of racing thoroughbred horses. Athletic performance of 119 racing Thoroughbred horses from Rio de Janeiro, Brazil, was calculated by assigning a point value for the results in racing (performance index (PI)), and serology for leptospirosis was conducted. A total of 85 (71.4 %) horses showed reactive titers (≥ 100), and of which 52 had high titers (34 with 400 and 18 with ≥ 800). Although those animals had high titers against Leptospira, no clinical signs associated with leptospirosis were observed. Seventeen (89.5 %) out of the 19 horses with substandard performance were seroreactive with high titers, in contrast with 35 % of seroreactivity in horses with good athletic performance (P < 0.0001). Additionally, seroreactivity to leptospirosis was more often observed in horses with substandard athletic performance in contrast to those with good performance (P < 0.0001, odds ratio 15.8). The Average PI of this group increased to 133 % after treatment (P < 0.0001). Leptospirosis may impair performance in racing horses, and antibiotic therapy may improve the performance of affected animals.