Horses may not require as much sleep as humans, but quality sleep is still vital for your equine’s overall health and well-being.

Although horses can sleep standing up thanks to their unique stay apparatus, REM sleep is only possible when they are lying down, and their muscles can relax.

Many factors can prevent a horse from getting enough quality sleep and lead to signs of sleep deprivation. Factors include pain, injury, health conditions, loud or bright barn environments, and even social hierarchy.

While equine sleep disorders are still poorly understood, horse owners should be aware of the signs of sleep deprivation in horses and take action to improve their horse’s sleep quality.

This article will review the current science on equine sleep patterns and the consequences, signs, and treatment of sleep deprivation in horses.

Equine Sleep Cycles

Little is known about equine sleep behaviour. However, research suggests that horses experience several different sleep patterns and that they cannot experience the full range of sleep cycles while standing. [1]

Like humans, horses go through several sleep cycles with different stages. These stages include rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. [12]

NREM Sleep

Researchers divide NREM sleep into four stages (N1 – N4) differentiated by brainwave patterns. The stages represent the gradual transition from wakefulness to sleep onset followed by deeper stages of sleep. [21]

Beta waves indicate full wakefulness, while slower alpha waves predominate during inactive states of relaxation. [21][11] Brain activity shifts to theta waves as horses enter N1 sleep. [21]

Most horse owners are familiar with the tell-tale signs of N1 sleep: a lowered head, semi-closed eyes, and a droopy bottom lip as the horse becomes drowsy and falls asleep.

Full sleep onset is marked by the transition to the N2 stage, with greater theta wave activity. This is the predominant sleep stage seen in humans and researchers routinely observe this stage in horses. [11]

Slow-wave sleep refers to the last two stages of NREM sleep, N3 and N4. These deep sleep stages are characterized by delta waves of slow oscillations, and high amplitude. [10][21]

Researchers have observed N3 sleep in horses but not N4. [11] Modern human research often combines these two stages. [21]