After a friend’s horse was badly injured in a trailer accident and had to wait at least two hours to be put down by a vet, I bought a gun, got my concealed carry permit, and researched bullet placement and angle (memorizing what needs to be done but printing for reference, as well).
In a perfect world, I would have a piece of property where predators live on the edge. The horses would be brought to the edge of the property, shot, and the bones collected a couple weeks later.
In the real world, I have two oldsters who are boarded. There is actually a crematory that will take entire horses a couple hours away and will pick up. If I have the day scheduled and can plan ahead, this will be the plan. Cost is about two months’ board. If it isn’t planned ahead, the renderer will likely be called. The barn is out of city limits, but I will need the barn owner’s permission to discharge a firearm on her property. I should get that in order - I want them to go on the property, not after a trailer ride to an unfamiliar location.
I feel much better about things when I have a plan and know what I will do. I don’t know when the end will come for my horses, but when it does I have plans A and B in place.