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HBO has run out of -- and out on -- "Luck." On Wednesday, the pay cable network, along with executive producers David Milch and Michael Mann, announced an abrupt end to the Dustin Hoffman-starring drama, following news that three horses had died during production.

Whether it was the threat of continued negative press, or that no one could guarantee another horse would not perish during the run of the series, the surprising and quick decision to pull the plug has caused many in the media to theorize as to why.

HBO cancels Luck after three horses die during production

When a third horse died Tuesday during filming for the second episode of the second season, HBO quickly announced that all use of horses on the show would be suspended indefinitely. (Two other horses died last year during the filming of the first season.)

But within the next 24 hours, after an investigation into further safety precautions had taken place, HBO and producers decided to kill the show outright, saying that they couldn't prevent further fatalities.

So why end things altogether?

California Horse Racing Board Equine Medical Director Dr. Rick Arthur, who worked with the production when it filmed at the Santa Anita race track, told TVGuide.com on Thursday that horse fatalities are not uncommon at the race track. "Accidents do happen," Arthur said. "It's not as outrageous as it's been played to be. Any of these accidents are not unique circumstances."

The third horse died, not while filming, but as she was being walked back to her stall. She reared, fell over backwards, struck her head on the ground, and the determination was made to euthanize her.

People for the Ethical Treatment of Animals, however, has long been opposed to the series. After HBO canceled the series, the organization sent out its own release, claiming "Luck" used "old, unfit and drugged horses."

Asked about PETA's claims, a rep for the network sent the following response: "The drugs that have been referenced by PETA were administered post-injury to calm the horse and to allow the attending veterinarian to properly examine the injury."

HBO, which worked closely with the American Humane Association and the CHRB, also insisted that no drugs were administered prior to filming of racing sequences for any purposes. PETA's Vice President of Laboratory Investigation Kathy Guillermo told TVGuide.com on Thursday that the necropsy report cited additional drugs in the horses' systems that shouldn't have been there, and has called upon law enforcement to investigate the deaths.

Is HBO's horse-racing series Luck a big gamble?

There may also have been future problems with shooting at Santa Anita, Luck's primary filming location.

Frank Stronach, chairman of the Stronach Group, which owns Santa Anita, said Wednesday he had wanted to end the relationship with the show. "I'm just disappointed because it puts sort of an ugly face on the whole point of horse racing," he told the San Gabriel Valley Tribune. "We're not going to participate if horse racing is shown in such a bad way."

Stronach had planned to meet with the producers, Santa Anita Director of Special Projects Pete Siberell told TVGuide.com. "[Stronach's] people in Toronto wanted me to set up a meeting with Michael Mann and David Milch to talk about the show. That was [Tuesday], when all this hit. We were going to have a meeting to talk about it because he was concerned about the direction the show was going."

A spokeswoman for HBO replied: "We have no knowledge of any such conversation."

Some industry watchers have said that the show's lukewarm ratings may have also been a factor to its quick demise. The show premiered to 1.1 million viewers in January, but fell by almost 50 percent a month later. However, HBO renewed the show for a second season early on, and has stuck by series with even smaller audiences, including its Laura Dern/Mike White comedy "Enlightened."

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