“How do you explain that, when other trainers — dealing with the same genetic pool of horses, racing over the same surfaces, and using the same vets — are having a substantially greater incidence of injuries?” she said. “That guy knew his horses better than anybody. They were professional athletes and he asked a lot of them, but he knew when he was asking too much.”

In 2010, O’Neill’s handling of a horse named Burna Dette was called into question by the California Horse Racing Board after he entered the filly in a bottom-level race at Los Alamitos racetrack. She broke down and had to be euthanized. In the span of two months, O’Neill had bought Burna Dette for $25,000, raced her at Del Mar, where she was well beaten, but then went ahead and two weeks later ran her in a race where she could have been bought for $2,000.

The investigation centered on whether O’Neill knew the horse was hurt and was trying to get rid of it. The board eventually determined it had “insufficient evidence to pursue any action” against O’Neill or his owners.

“It was a horrific event and hearing her name still brings chills to me,” O’Neill said. “I was trying to get her a win and work her back up the ladder.”

O’Neill, in his interview this week with The Times, said he would prefer to be speaking about the prospects of I’ll Have Another’s winning the 137th Preakness Stakes and perhaps then heading to New York for the Belmont Stakes and an opportunity to become the 12th horse to sweep the Triple Crown and the first since Affirmed in 1978.

But he said he also understood how, with his win in the Derby, his disciplinary record had fed the debate for a sport at a crossroads. O’Neill said he was trying to own up to his mistakes while fighting the allegations that he said were not true.

In the past, he said, he had succumbed to the pressure of racetrack officials who, eager to have full fields in their races, persuaded him to run horses that might have needed more rest. On Wednesday, however, he said, by way of example, he turned down the requests of officials at his home track of Hollywood Park to enter more than half a dozen horses for this Saturday’s races.

“In the past, I may have led a few over there that I knew didn’t have a chance to win to help them fill the race and me to maintain my stalls,” he said. “Last few years, I’ve been taking the approach of running less often. My horses are well taken care of, and I love them. And I love this sport.”