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]

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Equine Stay Apparatus

Horses can slip into light NREM sleep with little effort and remain standing up. This is due to the unique arrangement of their musculoskeletal system known as the stay apparatus.

The stay apparatus is a collection of ligaments and tendons that work together to keep the horse’s body upright with minimal muscular energy.

It works by locking major joints into place and stabilizing the limbs so the horse won’t lose its balance or fall over. [2]

Passive Stay Apparatus

Front limbs have a passive stay apparatus that involves the shoulder joint, biceps muscle, elbow joint, and triceps muscle. The biceps muscle prevents shoulder joint flexion while the triceps muscle fixes the elbow joint in extension. [2]

The Lacertus fibrosus tendon extends from the biceps tendon and attaches below the carpal joint to lock the limb in extension without using the muscles. The flexor tendons and suspensory ligament prevent over-extension of lower limb joints. [2]

Pelvic Stay Apparatus

Hind limbs also have a stay apparatus to stabilize the stifle, hock, and distal limb during rest. The stifle-locking mechanism consists of the distal patellar ligaments and the collateral ligaments of the stifle. [22]

Locking the stifle also stabilizes the hock joint through the reciprocal mechanism, which requires the stifle and hock to work in unison. The suspensory ligament and distal limb tendons stabilize the lower joints. [22]

The pelvic stay apparatus allows the horse to support its body weight without significant exertion. Horses will shift their weight while relaxed and cock one of their hind legs to rest the leg that isn’t bearing weight. [22]

REM Sleep

Although horses can enter light sleep stages while standing up, they cannot enter REM sleep without lying down in a lateral recumbent position. [11]

Most horses will lie down on their sternum (floor of the chest) during slow-wave sleep and only begin REM sleep once fully relaxed on their sides. [11]

REM sleep is a paradoxical sleep stage with a mixed frequency of low-amplitude brain waves also observed during wakefulness. This sleep stage involves the inhibition of spinal motor neurons to suppress skeletal muscle tone and reflexes. [21]

During this phase, the eyelids are closed, muscles relax, and rapid eye movement occurs. [12] Owners sometimes catch their horses dreaming during this phase and may notice facial twitching, limb contractions, or even vocalization in some horses.

While all stages of sleep are essential, REM sleep is vital for mental, emotional, and physical health. [12] If horses are unable or unwilling to lie down, a lack of REM sleep can harm their quality of life.

How Much Sleep do Horses Need?

Adult horses typically require between 3 and 6 hours of total sleep and 30 minutes of REM sleep in a day. [3]

Young foals require up to 12 hours of sleep per day and are even more susceptible to the harmful effects of sleep deprivation. [1]

Sleep cycles in horses can be as short as 15 minutes.

Horses are polyphasic sleepers, meaning they sleep multiple times throughout the day. However, most slow-wave and REM sleep occurs at night. [11]

Why Won’t my Horse Lay Down to Sleep?

There are several reasons why horses may not lie down to sleep. Some horses feel uncomfortable in their sleeping environment due to poor bedding, small stall size, or separation from other horses. [3]

Other potential causes include pain and stress. [5]  If your horse isn’t lying down to sleep, evaluate their environment and schedule a veterinary examination to determine if your horse has a sleep disorder and what may be preventing them from lying down.

Environmental Factors Influencing Sleep

Your horse’s environment can significantly impact their sleep quality.

Herd Population

Horses are prey animals that rely on constant vigilance to survive in the wild. If your horse doesn’t feel secure in their environment, their sleep quality will suffer. [11]

Living in herds allows individuals to take turns sleeping. If your horse lives alone, they may not feel safe enough to sleep. [11]

Herd dynamics also contribute to security. Wild horses generally have matriarchal hierarchies, and studies suggest domestic equines lie down more when a mare is on the lookout. [20]

Noise & Lighting

Horses in new environments often have greater vigilance during an acclimatization period to new stimuli. [11] Sensory stimuli such as bright light and loud noises can disturb equine sleep.

Light exposure regulates circadian rhythms and the production of sleep hormones. Studies observing domestic horses exposed to artificial light at night report a significant reduction in recumbency. [3]

Temperature

Like most mammals, horses also experience a reduction in core body temperature during sleep.  [11]

Owners could benefit from more research on the direct effects of ambient temperature on equine sleep. But anecdotal evidence suggests that over-blanketing may contribute to equine sleep disorders. [11]

Signs of Sleep Deprivation in Horses

Sleep deprivation is a significant welfare concern for horses, contributing to stress and a higher risk of health problems.

Sleep-deprived horses are at risk of serious injuries if they fall into REM sleep and collapse while standing. This also brings additional risk to their owners and handlers.

The symptoms of sleep disorders vary depending on the individual horse. Horses may experience sleep deprivation for two weeks before displaying clinical signs. [6]

Common signs to look for include: [13]

  • Collapsing into a bowing position
  • Sudden complete collapse
  • Lack of evidence of lying down (ie: no shavings in their tail or on their blanket)
  • Unexplained injuries on the fetlock, knee, or face
  • Increased drowsiness during the day
  • Hypervigilance
  • General poor performance

Installing a camera in your horse’s stall or paddock can also help you identify whether they are lying down and how often.

What Happens to Sleep-Deprived Horses?

During REM sleep, the horse loses muscle tone in their entire body including within the stay apparatus. [2]

Sleep-deprived horses will fall into REM sleep while standing up, causing their legs to buckle under them. [6] These horses collapse from fatigue and usually fall suddenly onto their knees.

Veterinarians define collapse as a loss of postural tone that may or may not lead to a loss of consciousness and recumbency (lying down). [14]

Other Causes of Collapse in Horses

Horses can also collapse for reasons other than sleep deprivation. If your horse collapses, immediately schedule a visit with your veterinarian to determine the cause.

Collapse can be caused by a musculoskeletal or neurologic condition. [14]

Cardiac conditions that cause a decrease in blood pressure and reduced blood flow to the brain can lead to an acute loss of consciousness, resulting in syncopal collapse. [15]

Sleep deprivation causes non-syncopal collapse, which is not associated with reduced blood flow to the brain. Horses maintain some degree of consciousness in this type of collapse. [14]

Other causes of non-syncopal collapse include seizures and hypoglycemia (low blood sugar). [16] Metabolic disorders such as hyperkalemic periodic paralysis may also predispose horses to collapse. [17]

Sleep Deprivation vs. Narcolepsy

Sleep deprivation and narcolepsy are equine sleep disorders that can lead to sudden partial or complete collapse in otherwise healthy horses. [18]

Unlike sleep deprivation, narcolepsy is an incurable neurological disease that causes excessive sleepiness and sudden attacks of REM sleep triggered by external stimuli. [4]

Equine narcolepsy is incredibly rare. Some researchers believe that the majority of reported cases of narcolepsy are misdiagnosed instances of sleep deprivation. [18]

Diagnosing Narcolepsy in Horses

Narcolepsy is challenging to diagnose in horses. [4] Consult your veterinarian to rule out other neurologic, musculoskeletal, respiratory, cardiovascular, and metabolic conditions before pursuing a narcolepsy diagnosis. [18]

If your veterinarian suspects that your horse has narcolepsy, they may use diagnostic methods developed to identify the condition in other animals. [19]

Your veterinarian may test your horse’s cerebrospinal fluid to look for abnormally low sleep hormone levels. [19].

Other methods of diagnosis include administering drugs that induce narcoleptic episodes in affected horses, but these results are not definitive. [4]

Types of Sleep Deprivation in Horses

Horses are affected by six main types of sleep deprivation, arising from environmental, physical, social, and emotional factors. [18]

If you are able to identify the root cause of your horse’s behaviour, management changes may be warranted for your sleep-deprived horse.

Pain-Associated

Physical discomfort is the most common cause of equine sleep disorders. [5]

This category includes horses diagnosed with painful conditions such as gastric ulcers and polysaccharide storage myopathy. [17]

This type of sleep deprivation may also affect senior horses with arthritis or mares in late pregnancy. [5]

Physical pain prevents horses from lying down to get enough REM sleep. Pain management, including joint injections, NSAIDs, and arthritis treatments may be warranted in these cases. [18]

Monotony-Induced

Horses placed in cross-ties for extended periods can experience monotony-induced sleep deprivation. [6]

Saddled school horses waiting for lessons, show horses tied for braiding, and police horses are often susceptible to this type of sleep deprivation. [6]

Environmental Insecurity

Environmental insecurity can cause psychological discomfort in a horse. If the horse does not feel safe enough to lie down, they may not get adequate REM sleep. [13]

If the root cause is identified by the owner and/or veterinarian, addressing the environmental issue will usually resolve this cause of sleep loss.

Even seemingly harmless changes in your horse’s management or routine can impair their sleep quality. Possible factors include stall relocation, stall-size changes, loss of friends, lighting changes, and inappropriate blanketing. [3]

Dominance Displacement

Some geldings can become excessively dominant in a herd environment. These horses may exert a lot of energy on constant aggressive behaviours. [20]

Focusing on dominance behaviours may prevent the horse from fully relaxing which can lead to sleep deprivation. [18]

Adding an alpha mare to the herd may resolve cases of sleep deprivation due to dominance displacement. [20]

Lyme-Disease Associated

Horses that test positive for Lyme disease may suffer from sleep deprivation even if they do not show clinical signs of physical discomfort or joint pain. [7]

Treating horses for the underlying disease may resolve the associated sleep disorder.

Sleep-Terror Associated

Recently, researchers and veterinarians have recognized sleep disorders in horses resembling human sleep terror behaviours. [8]

As more barns install night surveillance systems, veterinarians may identify more cases of sleep deprivation associated with night terrors in horses.

Management strategies may include medication. [18]

Diagnosis of Sleep Problems in Horses

After recognizing the clinical signs of sleep deprivation, veterinarians and horse owners can generally diagnose the underlying problem through process of elimination.

Investigations should begin with a veterinary exam to identify potential sources of physical pain. [18][15] Your veterinarian might perform a lameness exam, radiographs, or blood work during this phase.

A clinical exam can rule out physical causes of collapse and sleep deprivation, including pain, gastric ulcers, cardiac disease, and neurological problems.

If your veterinarian suspects that your horse is in perfect health, you should consider potential environmental factors. [3]

Keeping a daily journal of your horse’s routine, installing a camera in their paddock or stall, and recording when you notice signs of sleep deprivation can help you narrow down potential causes.

Examining your Horse’s Environment

Here are some questions that can help identify environmental causes of sleep loss in horses: [13]

  • Have the horse’s living conditions changed?
  • Are there new members in the herd?
  • Has the horse moved to a new barn or traveled to a show recently?
  • Is the horse required to stand still for prolonged periods?
  • Is the horse blanketed appropriately?
  • Has anything changed in the horse’s routine or feeding program?
  • Have there been any changes to the horse’s training program?

Treatment of Sleep Deprivation

If you suspect that your horse is sleep-deprived, schedule a visit with your veterinarian as soon as possible. You should also ensure that they have deep bedding in their stall to prevent injury.

Padded stable boots and wraps may help protect their legs in case of collapse. [3]

Medical Treatments

Prompt treatment is critical for addressing underlying medical conditions . Sleep issues should resolve once you address the primary problem. [18]

Sleep deprivation caused by musculoskeletal disease may resolve with joint corticosteroid injections and non-steroidal anti-inflammatories. [5]

Horses with gastric ulcers respond well to treatment with omeprazole and may also require dietary changes to prevent ulcers from recurring. [9]

dietary changes to prevent ulcers from recurring. [9]

Horses with sleep deprivation related to stress from moving to a new barn may respond to a few nightly doses of diazepam. The adaptogen Ashwagandha is also effective for anxiety. [23]

Management Changes

Ensure that your horse has a safe environment that enables them to achieve deep and restful sleep.

To support healthy sleep patterns, all horses need adequate shelter, appropriate social contact, ground conditions suitable for lying down, and a well-balanced diet. [11]

Also consider lighting, ambient noise, temperature, and air quality in your horse’s sleep environment.

It may take some trial and error to identify environmental factors contributing to your horse’s sleep issues. Not all horses respond to the same interventions.

For example, some horses maintained on pasture might need stabling for a period each day to completely relax, while others may feel claustrophobic in a stall. [13]

Older, arthritic horses often have difficulty getting up in winter and won’t lie down to sleep. Neoprene wraps over problem areas can help support and warm joints with reduced mobility. Mad Barn’s w-3 oil contains anti-inflammatory DHA which can help support joint health.

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Although it can take time to address management issues causing sleep deprivation, horses have an excellent prognosis once the underlying cause is resolved. [18]

Summary

  • REM sleep is essential for horses and only possible in lateral recumbency.
  • Many different physical, environmental, and psychological factors can make horses unwilling or unable to lie down, leading to sleep deprivation.
  • Sleep-deprived horses can suddenly collapse and injure themselves.
  • Identifying and addressing the root cause will successfully treat sleep deprivation in horses.

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References

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    4. Nieuwstadt, R. et al. Narcolepsy in horses. Tijdschr Diergeneeskd. 1993 View Summary
    5. Kelemen, Z. Recumbency as an Equine Welfare Indicator in Geriatric Horses and Horses with Chronic Orthopaedic Disease. Animals. 2021. View Summary
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    14. Lyle, C.H. et al. Retrospective Evaluation of Episodic Collapse in the Horse in a Referred Population: 25 Cases (1995-2009). J Vet Intern Med. 2010.View Summary
    15. Bonagura, J. Overview of Equine Cardiac Disease. Vet Clinics North Amer: Equine Pract. 2019. View Summary
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    17. Rudolph, J. Periodic paralysis in Quarter Horses: a sodium channel mutation disseminated by selective breeding. Nature Genet. 1992.
    18. Alemen, M. et al. Sleep and Sleep Disorders in Horses. AAEP Proceed. 2008.
    19. Nishino, S. et al. Effects of Thyrotropin-Releasing Hormone and Its Analogs on Daytime Sleepiness and Cataplexy in Canine Narcolepsy. J of Neurosci. 1997.
    20. Houpt, K. et al. Stability of equine hierarchies and the prevention of dominance-related aggression. Equine Vet J. 1980.View Summary
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    23. Priyanka, G. et al. Adaptogenic and Immunomodulatory Activity of Ashwagandha Root Extract: An Experimental Study in an Equine Model.. Frontiers in veterinary science. 2020. View Summary