An exercise rider takes a horse for a workout at Santa Anita Park with palm trees and the San Gabriel Mountains as a backdrop in Arcadia, Calif. (Jae C. Hong/AP, File)

Another horse was killed Thursday while training at historic Santa Anita Park in Arcadia, Calif., just one day following the reopening of the facility’s main track after experts investigating the surface could not identify a cause of the deaths.

Princess Lili B, a 3-year-old California-bred Filly, broke both front legs at the conclusion of a timed half-mile workout Thursday morning and was euthanized shortly after. She was the 22nd horse to suffer fatal injuries since Dec. 26 at the famed track. Broken bones in horses’ legs are often very difficult to heal.

Within hours of the incident, Santa Anita banned the use of whips and medications on race day. Among the substances banned is Lasix, an anti-bleeding drug that can open horse’s airways while running at high speeds, as well as nonsteriod anti-inflammatory drugs.

Belinda Stronach, chair and president of the Stronach Group, which owns the track, called the spate of deaths, “beyond heartbreaking” in an open letter

Training continued on the track after the incident, with the same additional safety measures that were instituted earlier this year after the spate of fatalities. Trainers are now required to request workouts for a particular horse with 24 hours notice, according to the Los Angeles Times, so veterinarians can prescreen horses for health concerns before they run.

“It’s tragic, but we stand fully behind the track, and we’re going to keep the track open,” said Tim Ritvo, chief operating officer of the Stronach Group (via Blood-Horse). “[Jockey] Aaron Gryder came to me and said he worked five horses today and all of them went over the track fine.”

Santa Anita has been planning on reopening the track to competitive racing on March 22. The track suspended racing last week as experts returned to inspect the surface of the main track and test soil samples, and had just begun allowing training again.

Santa Anita had been helping pay for horses to train at Los Alamitos and San Luis Rey Downs during the break.

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