All animals need sleep, and obviously horses are no different. But while we need to lay down to sleep, horses can sleep while standing up and while lying down, although they only enjoy REM (rapid eye movement) sleep, which is a very deep sleep, while lying down.
Horses require very little REM sleep each day – 30 to 60 minutes in total – and they can enjoy a light sleep while standing up. The benefits of sleeping on their feet include the ability to quickly become alert and galloping away from predators if needed. This is a survival mechanism for horses, due to their evolution as a prey species. It takes a fair amount of effort for horses to get up after lying down and the few extra seconds this takes could be the difference between survival and being caught by a predator.
Also as horses are large animals, if they were to lay down for extended periods of time, their blood flow would become restricted, resulting in further pressure on their internal organs, which is another good reason to stand up while they are sleeping most of the time.
Horses have a unique anatomical mechanism in their hind legs called the stay apparatus. This allows a horse’s patella or knee cap — located in the stifle joint — to pop out of place and lock the hind limb in a standing position. Although it sounds painful, it’s usually no problem for horses. When dozing while standing, this stay apparatus will lock in place in only one hind leg; the other hind limb will be relaxed. Often, the horse appears to be leaning on one hip as they doze.
There are three stages of sleep for horses, with deep sleep or “slow-wave sleep” being the second stage. Horses typically experience deep sleep while standing up. The third stage of sleep, REM, should only occur when a horse is lying down due to the need for complete muscle relaxation.
Most horses will only sleep for approximately three hours within a 24-hour period, although young foals can sleep for longer than adult horses.
A horse can only get enough sleep each day if they feel mentally and physically ready to sleep and are in an environment where they feel safe. If living out in a herd environment, often one horse will remain alert on their feet while other members of the group lie down to sleep.
If a horse is unable to get enough REM sleep, the horse may collapse as a result of the equine stay apparatus not coming into action when they fall into REM-sleep while standing, which can cause severe physical injuries. Reasons for a lack of REM sleep can include problems associated with the horse’s management or a physical problem that causes pain, especially if that prevents the horse from lying down comfortably or being able to rise easily.
Sleep deprivation in horses should not be confused with narcolepsy, which is a very rare chronic neurological disorder.
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