LOUISVILLE, Ky. -- A racehorse died Thursday at Churchill Downs after a freak fall that the trainer blamed on the sound of a starting gate bell blaring on the track's new sound system.

The 5-year-old mare Never Tell Lynda was walking toward the paddock on the track when she reared, twisted and fell, hitting her head, said her trainer, Kenneth Wirth. She died before the first race of the day at the track that's home to the Kentucky Derby.

A heartbroken Wirth later said the horse was startled by what Wirth thinks was the sound of a starting gate bell coming from a commercial on Churchill's massive new video board. The system includes 750 speakers.

"We teach horses to break from that," he said. "And you've got it on a loud speaker that everybody in a two-city block can hear. Well, what's she going to do? She thinks she's supposed to take off. And that's what she did. And when she did, she lunged and she lost her balance and went down."

The fall was not witnessed by any of the track veterinarians, but staff rushed to her aid, said Will Farmer, chief racing veterinarian for the Kentucky Horse Racing Commission.

"It was quickly evident that this horse was in the process of expiring," he said. "To ease her suffering, one of our veterinarians euthanized her."

A necropsy will be performed on the horse, but the clinical signs matched the trainer's description, Farmer said.

Wirth said the mare was being schooled, meaning she was not entered in the race but was doing a walk-through to prepare her for future races.

A Churchill Downs spokesman said the "extremely rare" schooling accident was heartbreaking.

"Our thoughts and prayers are with her connections," said track spokesman Darren Rogers. "We're currently gathering facts and talking with people about what might have led to Never Tell Lynda's accident. ... The health and safety of our human and equine athletes remains our highest priority."

Wirth said the sound system was "way too loud" at the time of the accident.

"The only thing you can blame is the music," Wirth said. "They've got to do something about it. ... The horses are the main thing here."

Another trainer, Dale Romans, said he hasn't seen any of his horses become startled by Churchill's sound system.

"It's one of those things, you try to think of everything," he said. "They just didn't think of this happening."

Romans said the track needs to "step up, do what's right and fix it" to prevent similar tragedies.

"We can't bring her back," he said. "All we can do, in her sacrifice, is to make sure that it never happens again."

The video board looming over the backstretch has become a new bragging point for Churchill.

The track's newest landmark made its debut in the days leading up to the Kentucky Derby this spring. Towering 170 feet over the backstretch, the high-definition, $12 million video screen is bigger than three basketball courts.

The horse's death is the latest in what's been a tough stretch for Churchill Downs this spring.

The famed track drew criticism from some of its fans for taking a bigger cut of the money bettors place on its races. The decision came after Kentucky lawmakers rejected the racing industry's latest effort to add slot machines to generate more cash to boost prize money for horse owners.

Hall of Fame jockey Ron Turcotte, who rode Secretariat to Triple Crown glory, said he skipped this year's Derby after being snubbed by the track's management. Turcotte, who is paralyzed, said he couldn't get a parking spot during his last Derby Day visit, and then couldn't even get into the track to watch last year's race. The track said any snub was the result of a "communication breakdown."

Then, Steve Coburn, co-owner of this year's Derby and Preakness winner, California Chrome, lashed out at Churchill Downs after the Preakness, which is held at the Pimlico Race Course in Maryland.

"Churchill Downs needs to call Maryland to get a lesson in hospitality," Coburn said. "These people right here, they've treated us like royalty."