Animal abuse (usually happening when filmmakers cut corners) is, sadly, nothing new in Hollywood. Go back to the Golden Age of Movies, where horses were made to fall by the brutal "Running W" method, i.e. the Errol Flynn CHARGE OF THE LIGHT BRIGADE from the 1930s.
Here's a definition of the "Running W'--http://www.omg-facts.com/view/Facts/46463
And it's sad to see that HBO, David Milch and Michael Mann apparently didn't do enough to protect the horses used on the now-canceled racetrack drama LUCK. Three dead horses are three too many.
I'll turn the floor over to commenter ScottyB on the DEADLINE.com site's thread about the end of LUCK:
"It’s really amazing that such a talented crew and creators weren’t able to create racing scenes that were a combo of CGI and stock footage. I really liked this show (but hey, I am one of the freaks who liked “John from Cincinnatti”) but they kind of deserved their fate after not finding a “work around” after the first two horse deaths.
In Battlestar Gallactica, they were able to fake space battles by showing Edward james Olmos moving ships around on a map, cutting to starfighters in cockpits and then cutting to stock battle footage.
The Mann/Milch team couldn’t figure out something similar with the thousands of hours of horse race footage in existence?"