Jamie Ness, the leading trainer at Tampa Bay Downs, will be allowed to start horses while state investigators test substances confiscated from his barn during a search on Tuesday, an official of Tampa Bay said on Wednesday. Margo Flynn, a spokeswoman for the track, said that security guards will be posted in Ness s barn as the investigation related to the search proceeds. Flynn said that unmarked substances confiscated during the search are being tested by the Florida Division of Pari-Mutuel Wagering to determine their composition. The investigation is being conducted by the division in conjunction with the Thoroughbred Racing Protective Bureau, a racetrack-funded security organization that conducted the Tuesday search of Ness s barn. Flynn said that the track would have no further comment until the investigation is complete. Ness, whose win total leads Tampa Bay s trainer standings and is eighth-best in the country this year, was at Presque Isle Downs on Tuesday and was not present for the search. Rules of racing typically prohibit trainers from having any controlled medications in their barns.