system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do horses get euthanized after injuries.

There was a report today that a former Kentucky Derby winner broke its leg and had to be euthanized. Why not give it the same treatment as dogs nag give it a cast? I assume it has something to do with the size of the animal, but isn't that roughly relative to what a dog would carry on a different scale?
gpt
Horses pretty much have to stand. Lying down causes circulation problems and lead to organ damage/failure. They also really need to distribute the weight properly over their 4 legs. Doing otherwise can lead to muscle damage and other problems.

Horses evolved in such a way that they stand for pretty much their entire life. They're not built to re-distribute their weight across 3 limbs like a dog or cat. A horse puts about 60% of their weight across their front legs, so damage to just one of their legs either means increased weight on the remaining front leg, or having to carry more weight on the back.