“Horses have appeared in many genres of film from the beginnings of the film industry, in historical films (such as Ben Hur and El Cid) and even in films about famous horses (such as Seabiscuit and Phar Lap), but they have been essential to Westerns ever since the first, The Great Train Robbery (1903). Many of these early Westerns required horses to perform stunts that could seriously injure or kill the animals;they were treated as disposable extras. Horses were regularly filmed falling to the ground thanks to trip wires, holes in the ground and other dangerous practices. These reached a head in the filming of Jesse James in 1939. To film a scene of a horse plunging over a cliff into water , the horse was put on a slippery platform that tilted so the animal went over the cliff and died. Following public outrage, the American Humane Association was given the right to set safety guidelines and monitor how animals were treated on sets. From 1966 to 1980 due to legal issues the American Humane Society lost some of its rights, but they were reinstated after a horse was killed due to unsafe explosives in the filming of Heaven’s Gate. Today horses are either trained to fall safely or perform a suitable stunt, although anything too dangerous can be achieved with an animatronic horse.” ——-Excerpt from ‘The Horse Book” by Kathleen Walker-Meikle.
Just as a side note to this Heaven’s Gate is renowned as a hugely expensive disaster costing many millions and was a total box office failure. But if any good came of it the death of the poor horse brought back regulations and oversight for horses and other animals in the making of films. Now you can see, in the film credits, that any animals used were treated humanely and not put at risk.