Mongolian Groom, who suffered a serious left-hind leg injury during the Breeders' Cup Classic on Saturday, was euthanized after being taken to an equine hospital at Santa Anita Park, according to a statement on the event's website.
It was the 37th death associated with the famed race track in the past 11 months.
"The death of Mongolian Groom is a loss to the entire horse racing community," race organizers said in the statement. "Our equine and human athletes' safety is the Breeders' Cup's top priority. We have worked closely with Santa Anita leading up to the World Championships to promote enhanced equine safety."
It is unclear how Mongolian Groom was injured. The news release said a world-renowned veterinarian, Dr. Larry Bramlage, will lead an investigation into the injury suffered by the 4-year-old gelding.
Mongolian Groom ran near the front of the 11-horse pack and was third when War of Will, on the rail, began to pass him in the stretch. War of Will jockey Tyler Gaffalione looked back just as Mongolian Groom appeared to break down.
The elite race was won by Vino Rosso, who was ridden by Irad Ortiz Jr. and trained by Todd Pletcher.
It was Ortiz's fourth win on the weekend and his first Classic win.
"He's a special horse," he told NBC Sports, which broadcast the race. "He's gotten good at the right time."
Ortiz said the race went as planned for the 4-year-old chestnut colt, who started from the 10th position and ran fourth much of the race. He motored down the stretch to win by 4.5 lengths.
"We were planning to stay three or four — fourth or fifth, I'm sorry, in the clear, don't want to be up inside the whole," he told reporters. "I thought the best race for him was to be in the clear, so everything worked out perfect."
There were no injuries in the other 13 races at the two-day event, billed as the world championships for thoroughbreds, with $30 million in prize money and awards.
Previous Classics won by star horses
Pletcher said safety was something he has been thinking about for a while.
"It's something that I think we were all very concerned about coming in," he said. "We were anxious for, not only running in huge races like these, but also hoping that everything would go smoothly and safely, and I think everyone took every precautionary measure they possibly could and, like I said, I just, I hope that it's something that he can have a successful surgery for."
Ortiz rode Horse of the Year candidate Bricks and Mortar to victory in the Breeders' Cup Turf, which had a total payout of $4 million.
"He would have to be right up there at the top. We never had a Horse of the Year, so if he's fortunate enough to get that award and for his body of work and for what he's overcome, all those things go into putting him right at the top as the best we have had," said trainer Chad C. Brown.
Bricks and Mortar edged United at the line of the 1.5-mile event by a head.
Historic track focus of controversy
This year marked 10th time the Breeders' Cup has been held at Santa Anita — and the first since 2016 — but the stunning course in Arcadia northeast of Los Angeles has been the focus of controversy this year.
Santa Anita, a celebrated and historic track which opened in 1934 and has been a favorite setting for the nearby film industry, closed for evaluation in March after more than 20 horses died in the span of three months.
When it reopened, there were numerous changes: Trainers had to apply two days in advance before working out a horse; jockeys had to replace whips with softer "cushion crops," and restrictions on steroids, anti-inflammation drugs and race-day medications were instituted.
The death toll rose to 36 last week, but course owner the Stronach Group insists equine welfare is paramount.
"The Stronach Group and Santa Anita safety measures put horse and rider safety above all else," it said in a statement last month. "[We] remain committed to leading transformative change in this traditional sport."
Among a host of safety protocols, equine health experts check on horses 72 hours before race day, they monitor all horses 24 hours a day, and they examine each runner three to four times the day before a race with all findings discussed among the specialists, say the organizers.
Speaking at the track Tuesday, Baffert said he had every confidence in the venue.
"I think it is safe," Baffert was quoted as saying in the Racing Post. "It is a different surface to what we had for the last Breeders' Cup here because they added some different material and changed it, but they have slowed it down trying to make it safer.
"It's deep and I think it's safe. I'm not worried about it. When it rained, some horses struggled with it, but I think they have got a hold of it now."
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