Louisiana regulatory and animal-health officials lifted a quarantine on a barn at Fair Ground racetrack on Thursday after tests from all 66 horses in the barn were negative for equine herpesvirus, track officials said.\nThe quarantine was placed on the barn on Dec. 26 after a horse trained by Dallas Stewart that had previously been in the barn tested positive for the virus, which attacks a horse's neurological system. The horse had first displayed symptoms of the virus on Dec. 23, and was shipped off the track's grounds the next day.\nThe quarantined barn contains horses trained by Stewart and Neil Howard. While the barn was under quarantine, both trainers were prohibited from entering horses or training with the rest of the horse population. Stewart entered two horses on Thursday for the Sunday card, while Howard entered one.\nFive horses in the barn have also been shipped off the grounds. Those horses will be retested on Monday, officials said, and if the tests are negative, the horses will be allowed to ship back on to the grounds.\nFair Grounds officials said that horses who ship in to the track will still need to comply with measures adopted during the quarantine. Those measures require horses to have a normal temperature reading, a certificate validating a veterinary inspection within the previous 48 hours, and a vaccination for herpes not fewer than 14 days earlier and not more than 90 days earlier.