I don't cut my apples. I also don't give a horse a whole apple either. Some apples, like granny smiths, can cause excess gas. So usually, I take one or two apples and walk down the barn isle and allow horses to take a bite out of it. I will hold onto it, watching my fingers of course, and wait patiently for them to work a chunk off. Guarantees they can't bite off more than they can chew.
And for the greedy ones that like to try and take off half the apple? I make them wait till last so they bite off half of a half.