Another horse—the fifth in three weeks—has died at the Del Mar racetrack in California. A 3-year-old gelding named Koa collapsed during training on Saturday and was euthanized, NBC San Diego reported. There were two deaths on Nov. 17, and two others on Nov. 10—just two days after the start of the fall season. The cause of Koa’s death is unclear; a necropsy has been scheduled.