Can Horses Sleep UpRight: Like humans, sleep is vital to a horse’s health. However, horses have unique resting patterns and characteristics. Horses are polyphasic sleepers, meaning they experience multiple sleep periods throughout the day, with the preponderance occurring at night. The horse’s sleep patterns depend on its environment, social hierarchy, age, diet, and familiarity with its surroundings. One unique quality of horses is their ability to sleep Upright!
How Do Horses Sleep?
The horse exhibits four stages of vigilance: wakefulness, lethargy, slow wave sleep (SWS), and rapid eye movement (REM) sleep. In SWS, the brain impulses of a horse are slowed and synchronized. During this period, the brain is not actively functioning. SWS can occur while the horse is standing or in sternal recumbency (lying on its torso with its legs folded underneath).
REM sleep is characterized by rapid and irregular brain waves similar to a state of wakefulness. During rapid eye movement (REM) sleep, a horse’s eyes swiftly move back and forth. In addition to eye movement, your horse may twitch his ears or skin, squint, flare his nostrils, and even paddle his legs. REM slumber occurs when the horse is lying lateral recumbent on his side. During rapid eye movement (REM) sleep, all muscles unwind and lose tone.
On average, horses spend between 5 and 7 hours per day napping. Approximately 15% of a horse’s total sleep duration is believed to be REM sleep. While some horses receive two to three hours of REM sleep daily, every horse requires at least thirty minutes.
There is no definitive quantity of time that horses can lay in lateral recumbency, but they can’t stay there too long. The horse’s weight alone exerts pressure on the body, restricting blood flow to vital organs and extremities. Additionally, the airways are compressed, which may result in abnormal breathing patterns. The pressure can also affect the horse’s nerves, resulting in temporary muscle paralysis due to nerve damage. When horses attempt to rise, they have trouble balancing on all four limbs, which can result in secondary injuries.
How Long Do Horses Sleep Upright?
As described above, most of a horse’s slumber occurs in the standing position and is classified as SWS. Total slumber time typically consists of cycles of sleep interrupted by awake periods. The stay apparatus, a unique anatomical feature of horses, enables horses to sleep standing up. A stay apparatus is a collection of tendons and ligaments that allow the horse to erect with minimal muscular effort. This is an excellent advantage for prey animals, such as horses, so they can rapidly awaken and flee in an emergency. In addition to resting in herds, horses utilize group sleeping as a protective measure. While the others slumber, they will rotate sentries or horses that will stand and remain vigilant.
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Can Horses Have Sleeping Disorders?
Understanding sleep disorders in horses is limited. The study of equine sleep disorders, including sleep deprivation, narcolepsy, and hypersomnia, continues.
Sleep deprivation is caused by a lack of sleep, which can occur during travel, a change in environment or routine (excessive commotion, unfamiliar conditions, insufficient bedding), or orthopedic or neurologic conditions that prevent a horse from lying down. Poor REM sleep can cause sleep deprivation in as little as 5 to 7 days.
Narcolepsy is a sleep disorder provoked by intense emotions and physical exertion. It is marked by excessive diurnal sleepiness and abnormal manifestations of REM sleep. Cataplexy and the advent of sleep may occur suddenly in narcoleptic horses.
Hypersomnia is a condition of excess sleep. However, this sleep is not restorative and usually doesn’t include REM sleep, leading to more lethargy. It may be the result of an underlying endocrine or neurological disorder.
Risks associated with insufficient equine sleep include:
- Poor performance
- Injury
- Aggressive behavior
Common signs of insufficient slumber in horses include excessive daytime drowsiness, abrasions on the knees and fetlocks (from collapsing episodes), reluctance or inability to lie down, and diminished athletic performance. A complete veterinary workup with video monitoring observations and continuous electroencephalography (EEG) is recommended to diagnose and treat a horse’s sleep disturbances.