According to the lawsuit, Casey says the AHA observed drugged horses, underweight and/or sick horses and the misidentification of horses by producers so that animal safety representatives couldn't track their medical histories.
"Luck" was canceled in March after at least three horses died during filming.
Casey is also suing the AHA and HBO for wrongful termination. She alleges she was fired in January 2012 after she tried to report the animal abuse to authorities.
"AHA bowed to political and financial pressure and refused to report the Production Defendants' conduct to the authorities," Casey says in the suit. "AHA instructed Plaintiff not to report such conduct. AHA engaged in efforts to conceal and cover up the production defendants' criminal activities."
HBO released the following statement to The Hollywood Reporter: "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. Barbara Casey was not an employee of HBO, and any questions regarding her employment should be directed to the AHA."