PHILADELPHIA — An embattled large-scale racehorse owner vowed to quit the sport amid a jockey boycott involving the condition of his animals.

Jockeys at Penn National Race Course in Grantville are refusing to ride against horses owned by Michael Gill after 10 of his horses broke down on the track in the past 13 months. Several jockeys racing on horses behind them have been thrown from their rides.

The Pennsylvania Racing Commission and Penn National have both opened investigations into Gill, a New Hampshire mortgage company owner who topped the industry's leader board last year with $6.7 million in earnings and 370 wins.

But it's unclear what will happen when racing resumes Wednesday night at Penn National.

Gill has horses entered in four races. Most of the jockeys in those races have scratched, leaving 36 horses listed without a rider.

Gill denied suggestions that he uses Penn National as a dumping ground to eke out a few final wins from cheap or late-career horses. He instead faulted the condition of the track, which races four nights per week throughout the often-harsh central Pennsylvania winter.

"Penn National has a history of that track being bad, and horses breaking down," Gill told The Associated Press on Tuesday. Gill said the most recent horse to break down, Laughing Moon, pulled a suspensory ligament in its leg when it hit an ice patch at the end of a third-place finish on Jan. 23.

Jockeys immediately huddled after the tragic finish — which sent several jockeys tumbling off their mounts and at least one to the hospital — and announced their protest, leading to a delay of the next race.

"Clearly, the jockeys and equine athletes should not be put in a position of participating in events that involve their health, safety and welfare, and where their riding strategy is compromised, until the commission's investigation is complete," the Penn National jockeys wrote in a letter to the racing commission on Friday. The Associated Press obtained a copy of the letter. About 30 jockeys are based at the track.

According to Gill, the necropsies conducted on Laughing Moon and a horse named Melodeeman, which broke down days earlier at Penn National, showed no wrongdoing. He insisted that he does not use any illegal drugs on his animals and said he takes good care of them at his training facility in southern Chester County.

"They won't even tell you the autopsies of my horses — they were clean, they were sound," Gill said, referring to the two deaths in January.

He noted that his horses at Philadelphia Park and Charles Town Races and Mountaineer Park in West Virginia have had no such problems.

Penn National plans to let Gill compete Wednesday unless the state concludes its investigation by then and says otherwise, a spokesman said. The track is trying to determine how to handle the shortage of jockeys, but said the condition of the racecourse is sound.

"I think the fact that the jockeys are pointing to Mr. Gill and not the track sort of speaks for itself," said Eric Schippers, vice president for public affairs at parent Penn National Gaming Inc.

Gill typically runs about five horses a night at Penn National, where he keeps 49 stalls. He had about 1,000 starts last year over 200 racing days, McErlean said this week.

Gill, who won the prestigious Eclipse Award in 2005 as the sport's top owner, has owned as many as 400 racehorses, but said he now has about 100. He plans to sell them off quickly and retire from the business, he said. But he predicts the breakdowns at Penn National will continue.

"The guys yelling the loudest will be buying the most," he said. "I'll sell them all. Then you watch these horses break down still."