Horses are polyphasic sleepers, meaning that horses will sleep in several periods during the day, most occurring during the evening. Like humans, horses really do need REM, or rapid eye movement, sleep, which occurs in deeper sleep. While we must lay down to sleep, horses can sleep standing and lying down, though they enjoy their REM (rapid eye movement) sleep, which is very deep sleep, only when lying down. In fact, many horses choose to sleep lying down over standing up, simply because it is far more comfortable.
However, if you spend sufficient time with horses, you will find that they may lie down for one of two positions. Even if they can sleep standing up, scientists believe horses need to still lay down to sleep every day. Adult horses mainly rest standing up, but they still have to lay down in order to get the necessary amount of REM sleep. The minimal time horses spend lying down for REM sleep shows horses ability to gain needed rest when standing.
REM sleep appears to primarily occur with a horse stretched out flat on its sides, not resting against its chest. Dozing-stand sleeping in the horse does not enable him to reach deep REM sleep, which he needs, as humans do. Horses can doze standing for several minutes at a time, and can lay down in deep REM sleep for hours.
Although horses require about two or three hours of REM sleep per night, this deep sleep usually occurs in 10- to 20-minute spurts. When horses do require deep sleep, however, they lay down, typically in a series of brief naps, totaling approximately two to three hours per day. Horses lie down to deep sleep fairly often, usually when little else is going on. Rather than falling asleep deeply each night, horses generally alternate their nights between resting and active.
Horses generally sleep in brief spurts during the night and throughout the day, ranging from as little as five minutes to as much as an hour (if unmolested). Even at night, when the horse is safely confined to his or her stall, a horse does not sleep longer than those brief stretches. Horses only will sleep that deep during the dark hours after midnight, unless a sleep disturbance occurs. You might have heard that humans need eight hours of sleep, but horses do not need anywhere close to that.
Where humans require anywhere from 8 to 10 hours of uninterrupted sleep each day, the requirements and patterns for a horses sleep are much different. Horses require much less sleep than humans (3-7 hours a day in adults, and even more in younger horses and older horses), not meeting this threshold has real consequences. Animals differ in how much sleep they require; cats, for instance, sleep for sixteen hours a day, whereas horses do less than three hours.
Horses are different from humans and many other animals, who spend a few hours sleeping at a consistent time every day. They sleep only about three hours in any 24 hour period, but they do not ever take long breaks, although younger horses can sleep longer than adults. As a herding animal, horses take turns lying down and sleeping well, while the other horses keep an eye out.
They may sleep only while standing, just like us humans might on a couch, but in order to get a proper rest (REM sleep), they have to lay down. Horses may be resting to some degree in standing, but to reach REM sleep, the deepest type of sleep, also called paradoxical or synchronized sleep, horses must lie down. Horses certainly can and do sleep standing up, but at some point, all horses need to lay down in order to reach the complete sleep cycle and to avoid sleep deprivation.
While horses may get quick naps standing, horses cannot achieve the REM sleep they so desperately need without relaxing all of their muscles. Even if horses in stalls with boxes are also able to take quick snoozes standing, horses clearly must lay down to rest and sleep at least part of the time.
Horses may get a brief nap standing, feed a bit, then sprawl on their sides for a few minutes of deeper sleep. You might not see them lying down a lot, since they mostly get their hard sleeps after midnight during dark hours of the night.
Your horse can nap briefly when standing, and often does, particularly if it is bored, but it will also lay down for better sleep at night. For most of those short naps, which usually last for thirty minutes or so, your horse stays standing. Other times, the nap is a short snooze, which you can tell by the change in the horses rear foot as the horse is sleeping standing.
Horses might not have to lie down to catch snoozing, but do have to sprawl on their sides during the few 10- 20-minute periods in the evening to get this RME sleep. A typical night with horses will include some feeding, standing dozes, and periods where they lay flat out to catch up on REM sleep, but only for brief sessions. Horses require 30 minutes to three hours of REM sleep a day, but this accounts for a very small portion of their resting habits. Horses only lay down for REM sleep in the horses deeper rest if they are really comfortable with their surroundings, confident in the dynamics of their group (if not in the barn on their own), and they feel like the other horses are going to be guarded as they get zzzs.
One key characteristic is their ability to stand for a nap; this allows them to get resty, yet stay standing, and be ready to bolt away should predators attack.