Louis O'Brien, the leading owner in North America with 221 wins in 2007, is in the process of disbanding his sizable stable and is leaving the sport after more than a half-century as a racehorse owner.\nO'Brien said Friday from his food distributorship business in St. Louis that he has wearied of the "aggravation that has become too much a part of the game," particularly with what has become of his hometown track, Fairmount Park in Collinsville, Ill.\nO'Brien, 73, had been the dominant owner for years at Fairmount, which traditionally had conducted racing virtually year-round before financial troubles led to the Illinois Racing Board assigning the track just three live dates for 2010.\nCampaigning mostly low-level claimers while employing Ralph Martinez as his only trainer, O'Brien remained prominent at other Midwestern tracks as Fairmount declined in recent years, including Hoosier Park in Indiana, where he was the leading owner each of the last seven years. O'Brien also ran horses regularly at tracks such as Hawthorne, Ellis Park, Turfway Park, Beulah Park, Prairie Meadows, and Indiana Downs.\nO'Brien said "a combination of a whole lot of things" has persuaded him to sell off all his Thoroughbred holdings, which at peak capacity consisted of about 75 active runners. \n"When the fun goes out of it . . . racing is not a money-maker, but I loved the game and I loved my horses," he said. "The last couple of years for me have been a financial disaster, and there are just too many problems in the game."\nO'Brien said he owned his first racehorse at age 18. Since 1976, the first year comprehensive statistics are available, he has won 1,520 races from 6,160 starts for earnings of $9,458,108. For three straight years leading up to his North American title in 2007, he was second in North America in wins, most notably 2006, when Maggi Moss ran a flurry of starters at year's end to take the title by a 211-206 count.\nMeanwhile, Martinez said Friday from Fairmount that he is rebuilding his stable from scratch and that he is willing to consider a number of tracks for his base of operations. Martinez, 32, has been training since 2000.