I had a mare who used to "cut" the dogs ran around the outside of the roundpen chasing the horse inside at a barn I used to board at. I always wondered if it bugged her and one day when I left her to herself and the dogs she basically looked like she was cutting them through the fence. They didn't like her form of the game and gave up...amazing what some breeding can do!
It's ironic, because most of us look at the horses racing on pavement and are SO horrified. And yet I bet those horses risk FAR less injury compared to the average American/Canadian Thoroughbred! Quite frankly, I would say running a horse on pavement is JUST as stupid as pushing a loaded down 2 year old as hard as you can! It's crazy how when things are "accepted" our perceptives change eh?