Laurel Park opened its backstretch on Wednesday after state agriculture officials confirmed that a second round of testing for the highly contagious diseases equine herpesvirus turned up no positive results.\nLaurel officials have prohibited horses from leaving the grounds of the racetrack since Nov. 14, when a 2-year-old filly named Nin tested positive for equine herpesvirus. The filly was euthanized several days later.\nLaurel's racing office was drawing entries on Wednesday for its Saturday card. The track's Thursday and Friday cards were drawn prior to the lifting of the prohibition.\nState agriculture officials tested all the horses stabled with the filly twice. None of the 25 other horses in the barn tested positive for the disease. In addition, 31 ponies at the track tested negative.\nOn Wednesday, the agriculture department lifted a hold order it had placed on the barn where the filly was stabled. Officials for the agriculture department said that it was highly unlikely any horses at the track were carrying the disease, citing a new, aggressive testing protocol.