I want to share a story before this gets too crazy.
I inadvertantly wound up with an old foundered shetland pony that I enjoyed for several years before she had to be euthanized because of chronic pain from founder. The vet arrived, and gave "the shot" based on the old ponies weight. Instead of her going peacefully to sleep, the pony started going bananas. I had to lay on top of her while the vet ran to her truck to get more drugs. Shetlands were bred to pull coal carts out of coalmines, they are tough. It was very unpleasant for me and I had nightmares about it for a long time.
Years later I purchased an enormous Belgian mare at an auction with the idea of breeding her to my Arabian stallion. She also was very foundered, but all I needed was ovaries I told myself. Three babies later and the founder had advanced to where she was laying down all of the time and in a lot of pain. This time I got a phone number from my vet for a man who for $125, picked up my giant friend, took her to his house, put a hood on her, and shot her directly in the forehead. She then went to a RENDERING PLANT. I don't understand in the course of all of the slaughterhouse hoopla this isn't ever brought up. Rendering plants take recently deceased animals. For this horse, almost 18 H, it made the most sense. Death was painless and instantaneous. She wasn't hauled to Canada or Mexico with no food or water, crammed in a trailer with as many other horses as can possibly shoved on. She was a wonderful gentle giant, and I miss her.