Horses’ sleep habits often spark curiosity, especially regarding whether they sleep with their eyes open. Unlike humans, horses have developed unique resting behaviors shaped by their evolutionary history as prey animals. These behaviors balance their need for rest with their instinct to remain alert.
Do Horses Sleep with Open Eyes?
Horses can sleep with their eyes open or partially open, typically during lighter slow-wave sleep (SWS) while standing. As prey animals, maintaining awareness is crucial for their survival, allowing them to detect threats and react quickly. A horse’s third eyelid, or nictitating membrane, provides protection and keeps the eye moist even when partially open during rest.
This ability is an evolutionary adaptation, enabling them to conserve energy while remaining vigilant. While their eyes may be open, their vision is somewhat impaired, allowing them to quickly become alert and flee if danger arises.
The Two Ways Horses Sleep
Horses utilize two primary postures for sleep: standing and lying down, each serving different sleep stages. When standing, horses primarily engage in slow-wave sleep (SWS), a lighter form of rest. This is made possible by the “stay apparatus,” a system of tendons and ligaments in their legs. This mechanism allows them to lock their major leg joints with minimal muscular effort, preventing them from collapsing while dozing.
While standing, their eyes can remain open or half-closed, enabling a swift response to any disturbance. However, to achieve deep, restorative Rapid Eye Movement (REM) sleep, horses must lie down. During REM sleep, their muscles relax completely, which is not possible in a standing position.
Lying down for REM sleep promotes muscle relaxation and proper brain activity. During this deepest sleep stage, horses typically have their eyes fully closed. While they need to lie down for REM, horses generally do not remain recumbent for extended periods, as prolonged lying can put pressure on their internal organs and restrict blood flow.
How Much Sleep Horses Need
Horses are polyphasic sleepers, taking multiple short naps throughout the day and night rather than one long stretch. Adult horses require approximately three to seven hours of sleep in a 24-hour period. Most of this sleep is slow-wave sleep, which they can achieve while standing.
Despite their ability to rest standing, some lying-down REM sleep is necessary, typically ranging from at least 30 minutes to three hours daily, often accumulated in short bursts of five to ten minutes. Factors such as age, perceived safety, and their environment can influence a horse’s sleep patterns. Foals sleep much more deeply and for longer durations than adult horses, often spending half their day sleeping when very young. Horses living in herds may take turns standing guard, allowing others to lie down and achieve deeper rest.