Tony Richardson says that several horses were killed prior to filming. Apparently their master-of-arms/stunt trainer was a maniac who tended to injure or even kill his horses while teaching extras how to sword fight. Richardson fired the trainer when he got wind of this. However, he says that no horses were killed or seriously hurt during the actual filming, and that they avoided tripwires; presumably this means they used trained stunt horses.
Actually watching the movie though, the horse falls are pretty rough-looking. Richardson could certainly be covering himself. I don't know what animal cruelty laws Turkey circa 1968 would have had.
The original Charge with Errol Flynn definitely killed at least dozen horses and one stuntman through reckless horse falls.
"Do you know what lies at the bottom of the mainstream? Mediocrity!"

Yes, from what I've heard. And, it seems a lot died.
Don't like what I'm saying? Then call 1800-Ima-CryBaby and ask for "Waaaaaa"