LOUISVILLE, Ky. - The jockey of Eight Belles said he felt his horse start to "gallop funny" yesterday after getting past the wire in the Kentucky Derby.

"I tried to pull her up, but she went down," Gabriel Saez, a 20-year-old from Panama, said just outside the jockeys' room at Churchill Downs.

A filly based at Delaware Park, Eight Belles had just finished second, 43/4 lengths behind the favorite, Big Brown, in this country's biggest horse race. Galloping out a good quarter-mile after it was over - part of the normal throttling-down after every horse race - Eight Belles went down because she had suffered fractures in both front legs. A bone had broken through the skin on her left leg.

She was euthanized immediately on the track, before her trainer even knew she had been injured.

His voice cracking, trainer Larry Jones later described how a shook-up Saez had told him afterward, "Larry, they put her down." Jones said he didn't comprehend what the jockey was saying, thinking Saez had misunderstood the situation.

"I said, 'How do you put a horse like this down?' Jones said. "Man, usually, they try to save them."

But Jones said he quickly got to his horse in the equine ambulance and saw the severity of the injuries.

"I checked her for myself," Jones said. "There was no decision to be made. She did not need to suffer - and she didn't suffer."

Jones said owner Rick Porter of Wilmington was "taking it pretty rough." Jones added, "We've taken criticism. We're going to be criticized and second-guessed. There is going to be somebody who will come up with 'That filly shouldn't have been in there.' I said that it wasn't the race. It wasn't the fact that 19 boys were in there. She never got bumped. She never did anything. She could have done this racing against Shetland ponies. It wasn't in the race where it happened."

Porter had said Jones originally was against running her in this race against 19 colts, but the trainer said during the week he was "at ease" with it. Afterward, Jones said that if Eight Belles had been showing stress getting to the line, he would have questioned himself severely for running against colts, but that wasn't the case.

No filly had run in the Kentucky Derby since 1999. Eight Belles was the 39th filly to race in the 134 runnings of the Derby and just the ninth since 1959. Three fillies have won it. The last was Winning Colors in 1988.

"In my years of racing, I have never seen this happen at the end of the race or during the race," said Larry Bramlage, the veterinarian answering questions at Churchill Downs, referring to injuries this severe after a race. "She didn't have a leg to stand on."

This was the latest tragic day for thoroughbred horse racing, a sport in which horses suffer lethal breakdowns an average of 1.5 times in every 1,000 starts, according to studies. But in the biggest races, that number has been higher lately. Most famously, Barbaro, the 2006 Kentucky Derby winner, went down in the Preakness Stakes and was euthanized eight months later when his injuries led to laminitis.

In last year's Breeders' Cup Classic, the sport's big season-ending race, a colt named George Washington broke down and was euthanized on the track at Monmouth Park.

On Friday, a 4-year-old colt named Chelokee, trained by Barbaro's trainer, Michael Matz, broke down during a race. As it turned out, Chelokee hadn't suffered a fracture in his right front leg as originally suspected, although the dislocation in the leg still makes his survival a 50-50 proposition, said Bramlage, who is in charge of Chelokee's care at Rood and Riddle Equine Hospital in Lexington, Ky.

"It's a really bad dislocation, five centimeters," Bramlage said yesterday morning at Churchill Downs.

Later on, Bramlage said it was "plausible and maybe even likely" that the fractures suffered by Eight Belles began as microfractures during the race, although there was no visible indication of that when she passed the wire. Jones, watching his horse closely, said he was "very pleased that she hit the wire running" and that he saw her ears up as she galloped around after Big Brown.

Asked about a move she made toward the rail late in the race, which caused Saez to switch his whip from his right hand to his left, Jones said Eight Belles had done the same thing in her last race, that she had picked up the habit of veering toward the rail.

"Many injuries to horses don't show up until they are cooling out," Bramlage said. "They get little cracks during the race, and we don't know it until they go to the wash rack and walk off and they are lame in one leg or the other."

Eight Belles was the first horse to be euthanized at a Triple Crown race since Prairie Bayou in the 1993 Belmont.

Bramlage was asked whether this incident suggests that it's perhaps dangerous for a filly to race against colts in a race as demanding as the Derby.

"I would say no," Bramlage said. "One injury is not an epidemic. As bad as it seems right now, it's one incident. Fillies race against colts on an intermittent basis, and it's not like we see this as a routine. In fact, I've never seen it before."

Jones hadn't gotten a chance to talk further to Saez, who was hurrying to catch a plane after the race.

"I was just saying, I did get to see my son yesterday and my daughter today, and I got to see Eight Belles every day - she was family, she was with us for the last year," Jones said. "Losing animals like this isn't fun. It's not supposed to happen. I don't know what to say - we're heartbroken."