Churchill Downs sees 8th horse fatality in 3 weeks.

Rio Moon, a 3-year-old colt, became the eighth horse to be euthanized at Churchill Downs in the past three weeks after suffering a catastrophic injury to his left foreleg during Sunday's sixth race. The track had already seen five horses euthanized after training and racing incidents leading up to the Kentucky Derby, and two more on the May 6 undercard. Churchill Downs has acknowledged the need to minimize avoidable risks in the sport.