ARCADIA, Calif. -- A filly broke both front legs at the end of a workout on the main dirt track at Santa Anita and was euthanized on Thursday, becoming the 22nd horse to suffer catastrophic injuries since Dec. 26.

Track ownership later announced a ban on race-day medication at the historic venue.

Trainer and owner David Bernstein said the 3-year-old named Princess Lili B broke down just past the finish line after a half-mile workout.

Bernstein told KTLA-TV that Princess Lili B apparently took a step as she changed leads, which led to her breaking her left ankle and then her right ankle. A lead change refers to which set of legs, left or right, leads or advances forward when a horse is galloping.

"She was always very sound and we've never had a problem with her," Bernstein said in the interview. "We didn't have to train her on any medication. She's just a lovely filly to be around."

The death occurred after several new safety initiatives were installed and racing suspended for two weeks.

Belinda Stronach, chairperson and president of The Stronach Group, which owns Santa Anita and Golden Gate Fields in Northern California, issued an open letter on the future of thoroughbred racing in California.

"What has happened at Santa Anita over the last few weeks is beyond heartbreaking," she said in the letter. "It is unacceptable to the public and, as people who deeply love horses, to everyone at The Stronach Group and Santa Anita."

Stronach announced what she called the "unprecedented step" of a ban on race-day medication at Santa Anita and Golden Gate Fields, which would make the tracks the first in North America to follow the strict International Federation of Horseracing Authorities standards.

The changes would include:

• banning the use of Lasix, which is used to prevent bleeding

• increasing the ban on legal therapeutic NSAIDS, joint injections, shockwave therapy, and anabolic steroids

• transparency of all veterinary records

• increasing out-of-competition testing

• increasing the time required for horses to be on-site prior to a race

• investment by The Stronach Group in diagnostic equipment to aid in the early detection of pre-existing conditions

• horses in training only allowed therapeutic medication with a qualified veterinary diagnosis

Stronch said the sport has reached a "watershed moment."

"We will wait no longer for the industry to come together as one to institute these changes," she said. "Nor will we wait for the legislation required to undertake this paradigm shift. We are taking a stand and fully recognize just how disruptive this might be."

Santa Anita had reopened its main track for limited workouts on Monday, with horses limited to jogging and galloping while the surface was monitored for any irregularities that may have caused the deaths of 21 horses since the winter meet began on Dec. 26.

Early reviews of the dirt surface had been mostly positive and there was cautious optimism that racing would resume later this month.

Shortly before Bernstein's filly was injured, Hall of Fame trainer Bob Baffert sent Kentucky Derby hopeful Roadster to the track for an uneventful workout.

In all, there were 75 workouts on the main track Thursday, down from 112 on Wednesday.

Bernstein said the filly's exercise rider didn't indicate any problem with the dirt surface.

"I think it's one of those things that happens, sadly enough," the trainer told KTLA.

Bernstein said he wouldn't hesitate to train another horse on Santa Anita's surface again.

"I know they've done the best job they can possibly do," he said. "They've hired a number of great experts to handle this surface."

This week's workouts were the first conducted under the track's new training protocols, which include two veterinarians observing each horse going to and from the track.