Another horse died Sunday at California’s Santa Anita track, marking the 23rd horse death at the track since Dec. 26—a remarkably high death toll that continues to puzzle officials. The Los Angeles Times reports Sunday that a horse named Arms Runner fell on the hillside turf course mid-race, injured his right front leg, and was euthanized soon after. Experts have tested the dirt at the facility to try and determine why so many horses have died, but there’s no conclusive answers yet. Arms Runner’s death comes just 17 days after the death of Princess Lili B, who broke both her front legs during a training session.