Chosen Vessel fractured his left front ankle on Saturday and was transported to the track's equine hospital for X-rays and diagnostics.
It was determined the 5-year-old gelding suffered an "an unrecoverable injury" and was euthanized based on the recommendation from the attending veterinarian, according to an incident report from the track.
Prosecutor finds no criminal liability in series of Santa Anita horse deaths
Officials at the company that owns Santa Anita Park say there are far fewer deaths in this meet compared to last year because of improved safety conditions. The current racing season began Dec. 26.
At least 45 horses have died at the facility since December 2018.
Santa Anita and the sport of horse racing have faced increasing pressure from animal-rights activists in connection with the horse deaths.
Animal rights supporters are lobbying to end horse racing in California.