The racing show's executive producers David Milch and Michael Mann announced on Wednesday (14Mar12) they were ceasing production of the programme after a horse was humanely killed following an accident at the studio's stables.
It was the third beast connected to the series to have died since filming began, prompting a campaign by officials at People for the Ethical Treatment of Animals (PETA) for an investigation.
And following the announcement the show has been cancelled, PETA bosses have called for a criminal probe into the deaths.
In a statement, a spokesman says, "PETA is glad that HBO has finally decided to cancel the show. We thank the whistleblowers who refused to let these horses' deaths go unnoticed. Should Milch, Mann, and HBO decide to start the series up again, PETA will be calling on them, as we have done from the start, to use stock racing footage instead of endangering horses for entertainment purposes.
"PETA has called on law enforcement to investigate the deaths of the horses used on the set and to bring charges as appropriate."