After a disquieting period in which seven horses died at Churchill Downs during the run-up to last week’s Kentucky Derby, horse racing is again caught up in a controversy, this one a doping case involving one of its biggest stars. On a rainy September afternoon last year, a colt named Forte eased into the starting gate of the Hopeful Stakes, an early and important race on the road to the Derby, at odds of nearly 7-1. He apparently relished the sloppy racetrack in Saratoga Springs, N.Y., unleashing a powerful kick in the stretch to win by a length. Shortly after leaving the winner’s circle, however, Forte was given a post-race drug test, which he failed but has yet to be adjudicated before New York regulators, according to two people who are familiar with the matter but are not authorized to speak about it. The positive test was for a substance used to relieve pain and reduce inflammation, according to those two people.

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