Arcadia, Calif. -- Santa Anita has canceled racing indefinitely to re-examine its dirt surface after the deaths of 21 horses in the last two-and-a-half months.

Tim Ritvo, chief operating officer of The Stronach Group, which owns Santa Anita, told The Associated Press Tuesday that racing won't be held this weekend, when two major races were scheduled: the San Felipe for 3-year-old Kentucky Derby hopefuls and the Santa Anita Handicap for older horses.

Ritvo wouldn't speculate on when training and racing would resume. After this weekend, races were to be run again starting March 14 at the storied racetrack slated to host the Breeders' Cup world championships for a record 10th time this fall.

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"In whole, we feel confident in the track and we're just being very proactive," Ritvo said. "We want to do all the testing that needs to be done. When we believe we're in good shape, we'll start to train over it again."

The Daily Racing Form first reported the cancellation.

The latest fatality occurred during training on Tuesday, when a 4-year-old filly got injured and was euthanized.

"Obviously, one horse is too many," Ritvo said. "The recent rash is just horrible. We need to definitely take a step back and evaluate everything."

Santa Anita received 11-1/2 inches of rain and had unusually cold temperatures in February, but it's unclear whether track conditions played a role in any of the fatalities.

The National Weather Service was forecasting 1 to 2 inches of rain in Los Angeles County starting overnight Tuesday and into Wednesday.

"We think that (rain) could definitely contribute even though our experts are telling us not," Ritvo said. "The tracks out here are built not for weather like that."

Ritvo said officials are "a little bit concerned" with the latest impending storm and how the dirt surface can change from muddy to fast in a short time.

A statue of Zenyatta stands in the paddock gardens area at Santa Anita Park on March 5, 2019, in Arcadia, Calif. Jae C. Hong / AP

Besides re-examining the dirt track, Ritvo said all racing protocols would be looked at.

"We won't rush it," he said. "Everybody takes a deep breath."

Ritvo was uncertain whether the San Felipe and Santa Anita Handicap would be rescheduled.

"Those are huge races," he said. "We hope so."

Seven deaths have occurred during races on the dirt oval at Santa Anita since the track's winter meet began on Dec. 26. Five have occurred on the turf course and nine came during training on dirt.

The highest-profile horse to be euthanized was Battle of Midway, winner of the 2017 Breeders' Cup Dirt Mile. The 5-year-old bay also finished third in the 2017 Kentucky Derby for Hall of Fame trainer Jerry Hollendorfer. The horse suffered injuries during a workout on Feb. 23.

Hall of Fame trainer Ron McAnally said 4-year-old filly Lets Light the Way "took a bad step or something" on Tuesday.

He said the injury was a shattered sesamoid in her right front leg. Sesamoid bones provide anchor points for the two branches of the suspensory ligament. The bones are under stress each time a horse takes a step. Lets Light the Way was X-rayed and later euthanized.

"I think the weather has a lot to do with it," said McAnally, whose wife, Debbie, owned the filly.

"Santa Anita has been a wonderful track, and they've done all kinds of tests," McAnally said. "I don't know what else they could do. It's a fluky thing."

Debbie McAnally told CBS Los Angeles, "It is a tragic loss, and weren't not too sure why it happened. We just need to get all the facts out there and go from there."

Also Tuesday, Vyjack was pulled up after completing a five-furlong workout, according to trainer Phil D'Amato. The graded stakes-winning 9-year-old gelding was taken off the track in a van. But D'Amato told the Daily Racing Form that Vyjack "took a couple of funny steps" and was OK.

The number of deaths has drawn both concern and criticism.

A handful of animal-rights activists gathered outside Santa Anita's main gate Sunday, carrying signs and shouting, CBS Los Angeles said.

PETA President Ingrid Newkirk agreed with the track's decision to close.

"This was the right thing to do," she said in a statement. "The track should remain closed until the California Horse Racing Board dumps the drugs entirely, or injured horses whose soreness is masked by legally allowed medication will continue to sustain shattered bones. PETA renews its call for a criminal investigation into the trainers and veterinarians who may have put injured horses on the track, leading to their deaths."

Ritvo said, "The first and most important thing is the health and welfare of the horses and jockeys."

In 2017, 20 deaths occurred among a total of 8,463 starts over a span of 122 racing days at Santa Anita, according to the most recent figures compiled by The Jockey Club. That's a rate of 2.36 deaths per 1,000 starts.

There were 1.61 deaths per 1,000 starts in the U.S. in 2017, according to the most recent figures from the Equine Injury Database, compiled by The Jockey Club. That was a slight increase in the rate of fatal injury compared with 2016, when there were 1.54 deaths per 1,000 starts.

The deaths were more frequent on dirt surfaces (1.74 per 1,000 starts) than on turf (1.36).

Santa Anita was closed for two days last week while the dirt surface was tested.

Mick Peterson, a soil and safety expert brought in from the University of Kentucky, proclaimed the track "100 percent ready" to resume racing.

Peterson said radar verified that all the silt, clay and sand, as well as the moisture content, were consistent throughout the track. Its dirt surface was peeled back 5 inches and reapplied.

Since Peterson's comments, two horses have died, including McAnally's filly. The 86-year-old trainer is one of the most respected in horse racing and has won three Eclipse Awards as the nation's most outstanding trainer.

Lets Light the Way had one win in four career starts and earnings of $18,500, according to Equibase. She last raced Feb. 2 at Santa Anita. McAnally purchased the filly for $15,000.

The other death occurred Saturday during the third race when 4-year-old filly Eskenforadrink was in the lead. Jockey Geovanni Franco pulled her up with an injury to her front leg. The filly was taken off the track and was later euthanized.

Fans left the track with heavy hearts, CBS L.A. said. "I love the sport, I'll always love the sport. But every possibility, every nickel should be spent to provide safety to the horses, the animals, the jockeys the trainers and in the sport as a whole," Paul Scherick remarked to the station.

Track officials announced Tuesday that a former track superintendent is returning immediately to Santa Anita as a consultant on-site as "a precautionary measure with regard to the condition of the one-mile main track." The consultant, Dennis Moore, worked in Arcadia from 2014 until retiring Dec. 31. He currently holds the same position at Del Mar and Los Alamitos racetrack in Orange County.

In 2014, Moore oversaw a major renovation of the dirt surface using sand that was dug up in the coastal suburb of El Segundo for construction projects at Los Angeles International Airport. The sand was screened for foreign materials and large rocks.

At the time, track officials said the reddish-brown sand would ensure balanced drainage during periods of wet weather and a consistent, safe cushion for horses year-round. That's important at Santa Anita, which added several weeks of racing to its schedule after the closure of Hollywood Park in Inglewood, California, in December 2013.