It was a thrilling finish: A long-shot named Mystik Dan held off a late charge by Sierra Leone and a colt from Japan named Forever Young on Saturday to win the 150th running of the Kentucky Derby, America’s oldest major continuing sporting event, bringing to a close a much-needed casualty-free week of thoroughbred racing.

It was a welcome conclusion for the multibillion-dollar sport imperiled by frequent racing fatalities, reckless breeding, dodgy doping practices and the old-fashioned greed of veterinarians, trainers and owners.

Last year, 12 horses perished at Churchill Downs in the days surrounding the famous race. It only got worse. Two weeks later, a horse trained by one of the sport’s most recognized trainers died at Pimlico Race Course. At the historic Saratoga Race Course in New York a few months later, another 13 horses died while racing and training at the sport’s signature summer meet, including two that seemed poised to win their races before they broke down near the finish line on nationally televised broadcasts.

Ambulances rumbled onto the track, emergency workers erected privacy screens and, behind them, vets euthanized the horses with injections. All of it put the social acceptability of one of America’s oldest sports at risk.

Why do racehorses die? As beautiful as a thoroughbred is in full flight, the legs that seemingly rarely touch the ground are fragile. Ankles the size of a Coke bottle and hooves the size of a crystal ashtray propel a 1,200-pound thoroughbred at speeds up to 35 miles per hour.