it can be hard for people to understand that every species of animal has a unique set of physical and mental needs, and that (FOR THEIR OWN BENEFIT) they should not be treated like human beings.
here's an example: when a horse breaks its leg, often the kindest thing you can do is euthanize it. that is because horses have lightweight bones that tend to shatter, rather than simply snap, and all those sharp pieces can sever blood vessels and nerves, which leads to tissue death. your average horse weighs 1,000 pounds. that amount of weight redistributed to 3 legs leads to pressure necrosis on the remaining hooves.
the reason the horse would require euthanasia isn't because it's life isn't the same as an able-bodied horse. it is because its leg would rot off and then its hooves would rot off and then it would die.
I currently have a broken leg, and will not be euthanized because I am a human being. if I had both legs amputated, I could still have a wonderful life, because I am a human being.
similarly, if my cat broke a leg, or had to have a limb amputation, that would be fine (well, not fine, but you get the idea) because she weighs 9lbs and could scurry about just fine as a tripod.
if you understand what an animal needs, you'll be better equipped to know when it has a fighting chance. you'll also know that sometimes, the kindest thing you can do is put it to rest.
Do we have a cue for laying down? no. But we have established the routine that it's the first thing we do when we enter the arena, may or may not bite me in the ass later 😂