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Why Horses Sleep Upright: A Simple Explanation

Ever noticed horses sleeping upright at night? This behavior is a survival strategy, balancing sleep needs with predator protection.

Horses, part of the prey animal lineage Equidae, sleep upright to evade attacks. “Being upright offers a surprise element against predators and a better escape chance than if they were lying down,” says Karen Waite, an equine expert at Michigan State University (USA).

Simply put, horses, being large creatures, require time and energy to get up. Thus, a horse standing is more prepared to flee upon waking. This is also true for other large herbivores and prey like zebras, bison, elephants, and giraffes, all capable of sleeping upright, as reported by Live Science.

But how do horses manage to sleep standing up? Horses possess unique anatomical traits, known as the “stay apparatus,” that enable them to sleep while standing. This includes tendons and ligaments in both front and back legs, says Waite.

When a horse relaxes its leg muscles, the stay apparatus’s ligaments and tendons act like tension bands, stabilizing the shoulder, knee, and ankle joints. This allows the horse to stand without much muscle tension.

Horses and REM Sleep While horses mostly sleep upright, they need to lie down for deeper sleep. “Horses mostly sleep upright, but they don’t achieve full REM sleep in this position,” says Sarah Matlock of Colorado State University.

During REM sleep, the brain processes new information into long-term memories. Lack of REM sleep can lead to mental focus and mood regulation issues, weakened immunity, and reduced cell growth.

Adult horses often manage with as little as 5 hours of sleep per day, mostly achieved while standing. However, a well-rested horse needs at least 25 minutes of REM sleep daily, only possible while lying down, says Matlock.

Hence, horses need to lie down daily. Otherwise, they risk sleep deprivation, posing a serious health risk, such as injury from falling, according to the American Association of Equine Practitioners. “Horses lacking enough REM sleep may be wrongly diagnosed with narcolepsy. For instance, they may fall while being ridden,” Matlock says.

Horses only lie down to sleep when they feel safe As sleeping upright is an adaptation to evade predators, horses need to feel secure before they’re willing to lie down to sleep, says Matlock. In wild horse populations, if multiple horses lie down simultaneously for REM sleep, at least one horse will always remain standing, likely to watch for potential predators.

“If they don’t feel safe in their environment, or they don’t have other horses with them, or if they’re isolated, then they’re less likely to feel safe enough to lie down,” Matlock says.

Image source: Shutterstock

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