Researchers offer advice on helping horses get quality sleep

Sleep provides horses an important rest and recovery period known to repair muscles, reinvigorate the immune system, and flush the brain of accumulated toxins.

Those are great benefits, but they come with a flip side: a significantly altered state of consciousness and physical readiness. And while horses can sleep standing up, they can only achieve rapid eye movement (REM) sleep while lying down—making these open-grasslands prey animals more vulnerable. That probably explains why horses evolved to need remarkably little sleep, says Linda Greening, PhD, senior lecturer in Hartpury University’s Equine Department, in the U.K.

Still, despite needing merely half the sleep we do—at least four hours will do—plus being able to take mini-naps throughout the day, researchers find it increasingly apparent that domestic horses lack sufficient sleep, Greening says. To better understand the problem, her team has just developed an equine sleep scoring system based on not only quantity but also quality.

What is good-quality sleep, and how much do horses need? How do you know if your horse is getting enough, and how can you improve it? In this article we’ll address those questions and more with helpful information and tips from leading equine sleep experts.

REM Sleep in Horses

A vital aspect of sleep quality is being able to achieve that dream-stage slumber known as REM sleep, says Katherine Houpt, VMD, PhD, Dipl. ACVB, professor emeritus at Cornell University’s College of Veterinary Medicine, in Ithaca, New York.

REM sleep is actually similar to wakefulness and tends to occur just before animals wake up, Greening explains. It’s during REM sleep that the brain “sorts out memories from the day,” selecting those to keep and those to delete, which “kind of frees up storage space,” she says. Horses need 40-45 minutes of REM sleep per 24 hours.

Standing horses can enter non-REM sleep—including a deep form of sleep—thanks to their stay apparatus that locks the legs. But because REM sleep induces a total loss of muscle tone throughout the body, it relaxes all soft tissues, including the stay apparatus. Horses can only safely enter REM sleep when lying flat on their sides (lateral recumbency) or up on their sternum (sternal recumbency), usually with their muzzle resting against the ground, Houpt explains.

The Seriousness of Sleep Deprivation in Horses

Although horses usually get their best quality sleep between midnight and 5:00 a.m., they don’t have to fulfill their sleep requirements all at once, our sources say. They can even go several days on reduced quantities of sleep.

The physical and mental effects of such short-term deprivation are unknown, they add. Researchers have shown that sleep deprivation over the long term, however, can cause more serious issues.

The most dramatic of these issues is collapse, Houpt says. Deprivation of REM sleep that lasts for more than a week or so can cause horses to drift into REM sleep even while standing. At that moment the stay apparatus releases and the horse collapses to the ground, she explains. This can cause pain and injury and interrupts that sleep cycle.

While often mislabeled narcolepsy—a sleep-related disorder with different causes—sleep deprivation leading to collapse can result in wounds on the knees and pasterns, Houpt says.

New evidence from research has led to suggestions that horses resisting collapse when drifting into REM sleep might actually get a minimal amount of such sleep, says Greening. “You get this characteristic bowing of the knees and wobbling around, and sometimes their noses might also touch the ground,” she explains.

Sleep-deprived horses could suffer other ill effects as well, such as lethargy or stumbling under saddle, says Greening. “So perhaps the horse is not being lazy,” she says. “He’s just not getting appropriate sleep.”

Houpt believes lack of sleep could also make horses irritable. “Is your horse pinning its ears back when it never did before?” she says. “Perhaps you should look for pain and/or lack of sleep.” And based on studies in humans and rodents, Houpt wonders whether gastric ulcers and other gastrointestinal issues might flare up in sleep-deprived horses. Meanwhile, in her current research Greening aims to investigate how regular, good-quality sleep affects horses’ learning skills, competition performance, and even their outlook on life—meaning how optimistic they feel.

Good Sleep: The Critical Comfort Factor

Horses seem to appreciate a soft, comfortable bed, which means either lush, dry outdoor grass or deep (4-6 inches), clean indoor bedding, says Houpt. Soft bedding cushions bones and joints and reduces pressure on muscles and skin, whereas harder surfaces make lying down and getting up painful. That is especially problematic for older horses that struggle with weakness and arthritis, she says.

Researchers have suggested horses sleep better on straw than shavings, says Houpt. But in either case, she adds, more is better especially when making old or arthritic horses comfortable.

Greening is currently discussing bedding depth recommendations with the U.K.’s National Equine Welfare Council. “Some people just use rubber mats, and they think that’s okay,” she says. “True, there’s evidence that certain horses will lie down on mats. But there’s also evidence that many horses won’t lie down on thin beds, and you’ll encourage more recumbency with thicker beds.”

Comfort also comes with a sense of security linked to an instinctive need to feel safe from wild predators. Unfamiliar noises, no neighboring horses in the barn, and unknown surroundings all mean the horse might not feel safe in the environment, Greening says.

Light plays a huge role in cueing sleep behavior in all mammals, she explains. “It is important that when the lights go out in a barn at night, they stay off,” she says. “Leaving them on or even turning them back on can interrupt biological and physiological  rhythms that have a negative impact on sleep quality.”

The Pros and Cons of Group Sleep

Some owners find that their horses sleep better when they’re near other horses, probably because of their nature as herd animals, Greening says.

In wild and feral herds there’s often one horse who stays watchfully awake while the others sleep, says Houpt. One of her students observed this behavior overnight in Przewalski herds, she says. She noted that the nighttime sentinel was often the stallion, who presumably caught up on his REM sleep in daytime bouts.

Group sleep in human-managed domestic herds, however, presents a far less idyllic image, notes Houpt. Studies show that even in well-designed, “active” stables with ample resources and resting areas, horses “walk all over each other,” she explains. “And guess who gets the longest sleep? The box-stalled horses. We’re always saying stalls are terrible nowadays. But the fact is, when you’re in a box stall, nobody’s stepping on you.”

Greening, meanwhile, has received reports that horses turned out to pasture just for the summer tend to lie down less. That might be due to hard ground, the change in routine, or the effect of the group.

Careful observation can help owners figure out which sleeping arrangements work best for each horse and herd.

Using Gadgets to Monitor Horses’ Sleep

An exciting thing about horse ownership today is the technology that allows us to monitor our horses. It lets us keep watch over them while we’re away and also “spy” on a species that often hides its weaknesses and vulnerabilities—an evolutionary adaptation to keep from looking like easy prey, our sources explain.

Today’s surveillance cameras make it simple for owners to capture their horses’ activities 24 hours a day, says Greening. Whether streamed live to their phone or stored on an SD card for later viewing—which they can watch at 2x or faster speed to save time—such video footage provides vital information about horses’ sleep quantity and quality. 

“Anyone who can afford a horse can afford a camera,” Houpt says. “And then you can see whether your horse is sleeping or not.” Importantly, people can only presume horses get REM sleep when they see the animals in lateral recumbency or in sternal recumbency with the nose or head against the ground. Cameras can capture horses starting to lie down but getting back up, which would suggest REM sleep is not being achieved, perhaps due to discomfort such as painful joints or an issue with the bedding.

“This would even be a great project for kids at Pony Clubs, finding out how much each horse or pony sleeps,” Houpt says.

While still mostly at a research level, electroencephalograms (EEGs) allow people to understand horses’ sleep cycles in finer detail, Greening says. She’s seeking funding for a study in which she and colleagues would use EEGs to measure sleep in high-level competition horses on an international scale. The findings could reveal both how well these athletes sleep and how their sleep cycles correspond to performance.

Commercial accelerometers placed on a horse’s feet, mane, or head might also provide useful information once their safety and benefits have been scientifically validated, Greening says. Now, however, these tools’ performances are limited to registering time in recumbency without providing data about REM sleep.

“I recommend the camera, which really helps recognize horses’ individual needs,” says Greening.

How to Help Your Horse Get Better Sleep

Improving your horse’s sleep starts with ensuring he has 4-6 inches of soft bedding, Houpt says. Offer him a large (greater than 10 feet x 10 feet) individual stall next to a friendly neighbor. This will let him feel socially secure without having to give up bed space and safe enough to lie down without getting cast.

Keep sleeping areas quiet zones, Greening recommends. Alternatively, try playing different kinds of soft music, or even nature sounds or various kinds of noise-drowning sounds like white noise. Researchers have shown that classical and country music, as well as nature sounds, make horses calmer, whereas jazz has the opposite effect. Greening’s team is currently researching the effects of such “audiotherapy” on horses’ sleep.

At their university’s yard Greening’s colleagues have recently introduced a schedule of routine daily rest times during daytime hours. This gives horses a predictable routine, when “they know there is going to be a time where they can safely rest or sleep if they need to,” she says.

“Based on research at Hartpury in collaboration with Equilume, the Royal Agricultural University, University College Dublin, and funded by the Morris Animal Foundation, we highly recommend ensuring lights are off overnight and that if you do need to check horses at night, using red light,” Greening says. Its wavelength won’t disturb horses’ sleep.

People can also try alternative therapies such as massage and nonflammable aromatherapies, says Houpt. “Nobody’s quantified the effects of those alternative therapies,” she says. “Just be sure to closely observe how they’re affecting your individual horse.”

Good sleep also requires appropriate feeding, Houpt adds. Horses with gastrointestinal pain due to high-starch, low-fiber diets might have disruptions due to discomfort, especially when lying on their internal organs. And because horses evolved to graze up to 16 hours per day, those without enough hay to last late into the night could wake up due to hunger.

Importantly, horses with ongoing sleep issues need veterinary evaluations to rule out all sources of pain, says Houpt. They might recommend a trial run of anti-inflammatories or pain relievers; if the horse lies down to sleep when on these medications, pain is likely the issue. Even so, it’s important to investigate what’s causing a horse’s pain to find a long-term solution, she says, because many medications can only be given short-term or lose efficacy over time. 

Finally, antidepressant and sedative drugs such as trazodone can help horses fall into a deep sleep—which can be especially useful for patients that avoid lying down due to chronic pain or traumatic experiences such as getting cast, she explains.

Regardless of the options people choose to improve their horses’ sleep, it’s important to continue video monitoring to observe the effects of different therapies and to adjust as needed, our sources say.

Take-Home Message

Compared to humans, horses don’t require a lot of sleep—but they need at least four hours a day, including 40-45 minutes of REM sleep, our sources say. Lack of sufficient quality sleep can lead to poor health and welfare and possibly poor performance, cognitive pessimism, and irritability. Owners should ensure their horses have secure, comfortable sleeping areas, monitor their horses’ sleep behavior, and try different approaches to address those lacking sufficient sleep.

This article was originally published in the Fall 2024 issue of The Horse: Your Guide to Equine Health Care.