BALTIMORE — On the eve of the 144th Preakness Stakes, a filly collapsed and died of an apparent heart attack suffered during the eighth race at Pimlico Race Course, a tragedy that marred Friday’s traditional Black-Eyed Susan Day and comes just as the sport was emerging from a shocking series of equine deaths in California over the winter and early spring.

Congrats Gal, a 3-year-old filly, died on the track Friday afternoon just after completing the Miss Preakness Stakes race. No cause of death was given, but veterinarians suspect a heart attack.

“Congrats Gal suffered sudden death after the eighth race today,” the Stronach Group, which owns Pimlico, and the Maryland Jockey Club said in a statement. “The incident occurred after the wire. Commission veterinarians attended to the horse immediately. Our thoughts go out to all of the owners, trainers and connections of Congrats Gal. The Stronach Group is committed to the welfare and safety of horses above all and we are saddened by what happened today. A full necropsy will be performed to try to determine the cause of death.”

The Canada-based Stronach Group is the same company that owns Santa Anita Park outside Los Angeles, where racing was abruptly halted for three weeks in March following 23 equine deaths in a three-month period. In its wake, Sen. Dianne Feinstein (D-Calif.) called for a suspension of all horse racing until the deaths could be investigated. A 24th horse died at Santa Anita on Friday, the first since racing resumed six weeks ago.

The occasional death of a racehorse is seen within the industry as an unfortunate but inescapable reality in a sport in which muscular, 2,000-pound animals race in all sorts of weather across distances of up to a mile and a half. In 2016, two horses died at Pimlico in separate incidents on Preakness Day.

“The sickening collapse and sudden death of Congrats Gal at Pimlico are proof that the Maryland racing industry has not done enough to protect horses,” Kathy Guillermo, senior vice president of People for the Ethical Treatment of Animals, said in a statement. “. . . We will be contacting the district attorney’s office, as we did in California, where the D.A. has appointed a task force to investigate training and veterinary practices.”

Friday’s eighth race at Pimlico, the Adena Springs Miss Preakness Stakes, was a six-furlong race for 3-year-old fillies with a $150,000 purse. The race appeared uneventful outside of Covfefe’s track-record time in winning by 8½ lengths.

But just after crossing the wire in ninth and last place, Congrats Gal — trained by Cathal Lynch for owner Charles Biggs — was quickly pulled up by her jockey, Trevor McCarthy, who dismounted just before the horse collapsed.

Libby Daniel, equine welfare and medical director for the Maryland Horse Racing Commission, attended to Congrats Gal on the track.

“I still thought this was a chance this was exhaustion-related,” Daniel said in a telephone interview. “The jockey was still there and saying: ‘Libby, she’s sound. She’s sound.’ ”

But after trying unsuccessfully to help Congrats Gal raise her chest — a common remedy for exhaustion-related issues — Daniel said she could no longer feel the horse’s heart beating.

“Her color was getting very pale,” Daniel said. “It was clear she was dying. . . . It’s something internal that just goes horribly wrong, and there’s no way to save them at that point.”

Daniel said Congrats Gal was given a standard examination before the race, and there were no problems detected then or during the post-parade or the early stages of the race, in which Congrats Gal ran as high as second.

“There’s no way to predict that anything like this is going to happen,” she said.

Congrats Gal’s death casts an even darker shadow over Saturday’s $1.5 million Preakness, the middle jewel of horse racing’s Triple Crown. The race is already without Kentucky Derby winner Country House, the first Derby champion in 23 years to skip the Preakness, as well as Maximum Security, the horse that crossed the finish line first at Churchill Downs — only to be disqualified for veering across multiple lanes of traffic, with Country House declared the winner after a 22-minute review.

In the aftermath of the controversial finish, owners, trainers and jockeys traded barbs over the stewards’ decision, and Maximum Security’s owner, Gary West, sued the Kentucky Horse Racing Commission to reverse the race’s official result. Jockey Luis Saez, who rode Maximum Security in the Derby, was suspended 15 racing days for failure to “control and guide his mount.”

The episode has left the sport worrying about attendance and television ratings for the Preakness — even as the race itself reaches a crossroads, with the Stronach Group pushing to move it from Pimlico to suburban Laurel Park, which it also owns, by 2021. Baltimore political leaders oppose the move and have threatened to take legal steps to stop it.

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