I guess the same thing as when people can no longer afford to feed their dogs. They get euthanized. Still, from what I’ve read, many times the horses suffer greatly being killed. It isn’t like a simple shot and they go to sleep and die peacefully.
Truthfully, I wish I had never seen the story.
It's no different than for cattle, pigs, chickens, etc.
Horses are livestock. If you can afford to treat yours like pets and want to feed them until they die of old age, that's your business.
But once the owner of a horse can no longer afford to pasture and feed it, which is happening (by design) all the time under Ubama, what do you suggest happens to it?
PS - Under Ubama, suicide is the leading cause of death. It ain't just horses he's killing.
Most of the time the irresponsible horse owner that is the most to blame for the thousands of unwanted horses will not or cannot pay to get them euthanized, usually they starve them in their backyard or dump them on others or to fend for themselves and starve.