Sleep is vitally important to horses, but equines don’t require the eight consecutive hours many humans need to be healthy and rested. Instead, the average horse will spend just under three hours per day asleep; this sleep will be spaced out throughout the entire 24-hour time period. It’s rare for an adult horse to spend over 10 minutes asleep at any one time. This means that a horse sleeps between 15 and 21 times a day.
Horses can sleep standing up using a “stay apparatus” that effectively locks their legs in place using a group of ligaments, tendons and muscles. As horses are prey animals, using this mechanism allows the horse to move quickly if any predators are around. Generally, a horse that is resting on three legs is dozing and not actively asleep. When standing, horses tend to keep one or both eyes open, even while dozing. This also allows him to react quickly should a predator threaten.