Now, the pay-cable network is being accused of trying to hide their alleged inhumane treatment of the animals.
Barbara Casey, who worked for 13 years as the director of production for the American Humane Association's film and television unit, is suing AHA, HBO and the show's producer, Stewart Productions, claiming they tried to cover up the alleged abuse and safety violations.
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Per the lawsuit filed in Los Angeles Superior Court and obtained by The Hollywood Reporter, Casey also alleges AHA wrongfully terminated her after she blew the whistle on the horses' perilous situation.
The complaint states that the animal-welfare organization witnessed drugged horses that were oftentimes sick and underweight routinely used on Luck while officials colluded with producers and looked the other way.
That was due, she contends, to HBO and Stewart Productions pressuring AHA hierarchy to let them violate safety standards "in order to save time and money" and "minimize any disruption to its production schedule."
According to the employee, that resulted in animal abuse and cruelty observed by the AHA, allegedly in the form of horses that were drugged to perform; defendants "intentionally misidentifying horses so that the humane officers and/or safety representative could not track their medical histories"; and, on one occasion, interfering in the reporting of an equine named Hometrader that had died.
"AHA told its representatives not to document this horse's death because he was killed during a summer hiatus from filming and therefore did not count," read the complaint.
The suit claims the AHA ultimately ignored Casey's protests and her wish to report the horses' abuse to authorities. Sure enough, she says, she was fired in January 2012, purportedly in retaliation.
Casey's suit seeks general and punitive damages.
For its part, HBO denies the allegations.
"We took every precaution to ensure that our horses were treated humanely and with the utmost care, exceeding every safeguard of all protocols and guidelines required of the production," the network said in a statement. "Barbara Casey was not an employee of HBO, and any questions regarding her employment should be directed to the AHA."
A rep for the AHA was unavailable for comment.