I used to have a horse. I miss her a lot. She was deemed crazy, partially due to past abuse. Between that and a horrible skin condition that made her very uncomfortable I made the decision to have her humanely euthanized instead of selling her off to be a broodmare, or worse, dog food. At least she had a good life with me. Then my family also had a couple of very old Arabians that eventually coliced (due to age). Ah, every time I deal with horses it ends up a tragedy it seems. :/
On the other hand, I was very interested in natural horse keeping. No shoes, no forceful methods. So I like to think the horses that came and died with us had peaceful final days. Some day I will have a horse again, but that will be many years from now.