Horse racing is a sport that developed from the ancient practice of connecting horses to two-wheeled carts or chariots and competing in a contest of speed or stamina. Over the centuries it has grown from a primitive game into a modern spectacle involving thousands of horses, sophisticated electronic monitoring equipment and vast sums of money. But the basic concept remains unchanged: the horse that crosses the finish line first is the winner.

The sport is not without controversy: Animal-rights activists suggest that many horses don’t enjoy running and that they are subjected to a constant barrage of stimulants in order to run fast enough to win. Even if they enjoy the experience, horses can become overextended and suffer gruesome breakdowns and injuries. But the industry claims that horses are well cared for and stoic, and that improvements in medical treatment and technology have made the sport safer for both participants and spectators.

At Santa Anita, drenched in pinkish light, the pack was moving with huge strides and hypnotic smoothness. In the backstretch, War of Will was hugging the rail, but he looked tired as he entered the far turn, and soon he began to fade, allowing McKinzie and Mongolian Groom to surge past him. Then, at the top of the stretch, a chestnut colt named Vino Rosso moved up on the outside. Sixty-eight thousand humans switched from cheering to shrieking.

As the race continued, you could see that both horses were hurting, but they kept going. A horse’s lower legs take a brutal beating when they sprint down a track at such speeds, straining tendons, ligaments and joints. One of Mongolian Groom’s hind legs was wrapped in blue bandages, and his jockey used a heavy-blue hood to keep him concentrated on what was ahead and a shadow roll across his nose to help reduce the number of people he would have to startle (horses can kick themselves when they’re nervous).

Both horses were injected that morning with Lasix, a diuretic noted on the racing form by a boldface “L.” The drug is supposed to prevent pulmonary bleeding that hard running sometimes causes, but it also makes them unload epic amounts of urine—twenty or 30 pounds worth.

The track’s management and Breeders’ Cup officials were desperate to have the event go off smoothly, and they were pleased when it did. But the day after the race, an activist group called the End Horse Racing Subsidies Coalition released a report that suggested that Lasix was actually masking an enormous problem in thoroughbred racing: sloppy breeding and excessive use of performance-enhancing drugs. The report was based on interviews with dozens of trainers and veterinarians, and it included an investigation into how thoroughbreds are injured and die. The group’s recommendations are aimed at bringing the United States closer to Europe and other venues in terms of basic horse-racing safety.