Travis Dunkelberger, the nation's leading jockey with 259 wins, broke his collarbone Wednesday night at Charles Town Race Course and is expected to miss four to six weeks of riding according to his agent Steve Rushing. "It was the seventh race and the horse (Southern Trail) took a bad step and tossed Travis," said Rushing. "He is scheduled to visit a specialist tomorrow (Thursday) to see if surgery will be required." Riding in Maryland for Dale Capuano, Dunkelberger has crossed the finish line ahead of the pack 145 times at Pimlico and Laurel Park this year. Rushing indicated that Capuano will use Ramon Dominguez, another Rushing client, as his main rider until Dunkelberger returns. Dominguez began the day two wins behind Dunkelberger in the jockey standings with 257 victories. Last year, the 24-year old Dunkelberger was the fourth leading rider in the country with 352 wins.