Third Horse Killed in Luck Animal scenes suspended again in controversial HBO series By Mary Papenfuss, Newser Staff Posted Mar 14, 2012 12:01 AM CDT 17 comments Comments A scene from the HBO horse-racing series "Luck." A third horse used in the series has been put down after suffering an injury. (AP Photo/HBO, Gusmano Cesaretti) (Newser) – A third horse in the HBO horse-racing series Luck has been put down after suffering an injury. The death has triggered suspension of horse scenes, again, over concerns about animal treatment. The humane association that oversees Hollywood productions demanded that "all production involving horses be shut down." The American Humane Association is also insisting that the suspension remain in "full effect pending a complete, thorough, and comprehensive investigation." The horse was being led back to a racetrack stable at Santa Anita Park when it reared and fell back yesterday, striking its head, reports AP. The series, probing the seedier side of racing, is in its second season. Two horses were put down in the first season after suffering injuries while racing. New protocols were put into effect after the second death, which were being followed yesterday, said HBO officials, who added that they were "deeply saddened" by the death. An investigation is continuing.