The Significant Seven - John McEvoy

Seven lifelong friends and racing fans from their student days at the University of Wisconsin strike it lucky at Saratoga Race Track when they combine to win a plus million dollar Pick Six. They subsequently use some of those profits to buy race horses, one of which, The Badger Express, turns out to be a sensational runner, stallion, and money maker. Seven years later, the men become targets of a professional assassin, an ex-Navy SEAL and Iraq private security guard named Orth. They begin dying, one by one.
Jack Doyle returns to the race track, volunteering to aid FBI agents in a search for criminals fixing races. Doyle then becomes involved in protecting Rene Rison, the favored daughter of the Significant Seven's leader Arnie Rison.
Jack Doyle, as always irreverent, observant, opinionated, sometimes mistaken but always persistent, eventually manages to find answers to the questions of who is
fixing the races and who is having members of the Significant Seven killed off.