(CBS NEWS) -- "Luck" has run out of luck.
Cable giant HBO dropped its new horseracing drama Wednesday after three horses died during production.
"Luck" had just begun shooting a new season.
The series told the story of the seedier side of professional horseracing. The sleek beauty of the animals on the track was matched by the skill of A-list actors Dustin Hoffman and Nick Nolte.
But now, the thoroughbreds, once stars of the show, are out of work.
HBO abruptly scrapped "Luck" in the wake of three horses dying on set. Two were put down last season after fracturing their legs. The third died after it reared up and hit its head.
In a statement, HBO said, "While we maintained the highest safety standards possible, accidents unfortunately happen, and it is impossible to guarantee they won't in the future."
HBO may contend the deaths resulted from accidents, but the animal rights group PETA says they were accidents waiting to happen. PETA says whistleblowers contacted it during the first season of "Luck," but PETA's complaints of animal mistreatment went nowhere -- even after the deaths of the first two horses.
"We got the necropsy reports on those horses through a Freedom of Information Act (petition)," says PETA's Lisa Lange, "and what we found was shocking. One of the horses had been pumped full of painkilling drugs, another one was old and arthritic"
But doctors who oversaw the horses say PETA is misreading the death report, and that the painkillers were given to one horse to calm it down after its leg injury.
Dr. Rick Arthur, a veterinarian at the Santa Anita racetrack in California, told CBS News, "HBO did everything they possibly could to ensure the safety of those horses."
The series was gaining ground with critics and was shooting episodes for season two.
But its ratings - just half-a-million viewers -- were disappointing. Variety Associate Editor Jon Weisman wonders whether the ratings race was the real reason the show was pulled. "There's going to be a lot of speculation that that's exactly what happened -- that they used this for cover to get out from a show that they perhaps didn't really want to be involved with long term," he says.
The American Humane Association, which monitors animals on TV and movie sets, said cancelling the series is "arguably the best decision HBO could have made."
PETA has called for a criminal investigation of the latest horse death.