It’s part of their survival
The root of horses sleeping while standing comes from their days in the wild and their “fight or flight” response. Rather than fight like some animals do when attacked, horses, being herbivores, are more inclined to flight, or run, from their predators. Since they have a difficult time standing up once they lay down, standing gives horses a higher chance of survival.
Horses can relax while standing
Remarkably, their bodies are also biologically designed to sleep while standing. Horses have a “stay apparatus”, which is a system of tendons and ligaments that keep the horse in the standing position while their muscles are able to relax. In their front legs the stay apparatus is always intact, but in their hind legs a horse has to rotate their hip and hook one bone over a knob of another bone to put the stay apparatus into effect. The stay apparatus not only allows the horse to stand for long periods of time, but to stand comfortably — a radical difference from our muscles that contract and ache after standing thirty minutes too long.
They still need to lie down sometimes
However, horses aren’t devoid of the need to lie down and sleep, as horses — just like us — need rapid eye movement (REM) sleep, and without it, it will eventually lead to their death. Yet the average eight hours of REM sleep we need a night is hardly the same for a horse, who on average needs 15-20 minutes a day, or an hour or two every few days, depending on their age and if they’re domesticated.
Horses will always wait to get their REM sleep until they feel safe, which is why domesticated horses often get more REM sleep than wild ones. Though you still won’t see your average family horse lying around for too long, as horses who spend too much time lying down can constrict blood flow to the large muscles in their legs, making standing up again very difficult.
In the wild, where horses get the least amount of REM sleep, it’s common for other horses to sleep while standing, allowing one horse to sleep lying at a time and ensuring they’re ready to run if a predator gets near.
Sleeping while standing has its benefits
The next time you pass a horse standing up he might be sleeping. And don’t feel too bad that they have to sleep standing, in fact, maybe you should even feel jealous. . . Who wouldn’t want to take a quick snooze while waiting in a long line at the DMV or grocery store.