Horses average two and a half hours of sleep every 24 hours, if conditions are ideal.
Your horse can run, but he can't hide...sleep must come eventually
Sleep is like money: If you have enough, you don’t tend to worry about it. But if you’re caught short, it can haunt your every waking minute. And the same is true for your horse, to an extent.
Horses and most grazing animals sleep an average of two and a half hours every 24 hours, if conditions are ideal and the environment is secure. Most of this sleep is amassed by “nickel and diming,” meaning horses can snooze for short periods—about 15 minutes at a time. Those minutes all add together to comprise that overall sleep total. Horses can go weeks without a full sleep cycle when needed, however, which is in direct contrast to humans who require prolonged periods of undisturbed sleep to function optimally.
“Considering how important and well-studied sleep is in humans and other species, surprisingly little is actually known about sleep disorders in horses,” notes Joe Bertone, DVM, MS, Dipl. ACVIM, professor of equine medicine at Western University of Health Sciences’ College of -Veterinary Medicine, in Pomona, Calif. And equine sleep isn’t something people think about much.
To prove this point, Bertone asks horse owners, “Have you ever wondered if your horse is getting enough sleep? Do you know how many hours of sleep a horse should get, and how much of that sleep can be achieved on four feet?”
Data on both normal and abnormal equine sleep habits is fairly limited, but in this article we’ll unpack the most up-to-date, detailed information on how horses sleep, along with what happens when their passage to ponyland is disturbed.
“Normal” Sleep Patterns
Observations from the 1960s and ’70s indicate that horses have four phases of sleep: diffuse drowsiness, intermediary, slow-wave, and paradoxical. Diffuse drowsiness often occurs when horses stand with their front legs parallel (square) and their head and neck lowered slightly. They display a downward gaze with relaxed eyelids, ears, and lower lip. They frequently rest a single rear leg by carrying the hind-end weight with the other rear limb.
In the intermediary phase, just before lying down, horses become alert and examine their environment. Then they lie down if they feel safe enough to do so. Once lying down, horses experience diffuse drowsiness again and, if at ease with their surroundings, enter into slow-wave sleep. When drowsy, horses often lie sternal (on their abdomen with tucked-under legs) with their head slightly raised; they can be easily aroused from their slight slumber at this point. In general, horses will then lie on their side to move into slow-wave sleep.
“Importantly, paradoxical sleep requires a horse to lie down because all muscles relax,” says Bertone. During this phase, rapid eye movement (REM) sleep occurs and the horse’s brain is very active, but he is essentially paralyzed; he generally remains in the sternal position, but moves his head to the side and to the ground to remain propped up. Bertone says horses likely prefer this sternal posture because it’s easier for them to breathe than when they are lying on their sides.
Recently, a pair of researchers from the Institute of Animal Welfare, Ethology and Animal Hygiene at the Veterinary Faculty of the Ludwig-Maximilians University, in Munich, Germany, examined 10 horses’ sleep profiles. Those researchers, Anna-Caroline Wohr and Michael Erhard, used a somnographic unit capable of recording an electroencephalogram, electromyogram, electrocardiogram, and electro-oculogram, which measure electrical activity in the brain muscle along with heart and eye movement.
The researchers confirmed that horses do experience these four distinct sleep phases, and each phase is short and interrupted frequently by waking phases. They also observed that early slow-wave sleep did not necessitate lying down.
Based on his work with collapsing horses and sleep deprivation, Bertone believes sleep deprivation behavior occurs because horses either do not have sufficient time to lie down for curcial paradoxical sleep, or they refuse to do so (for various reasons). And other equine sleep researchers attest that horses that either can’t or aren’t permitted to lie down become sleep-deprived.
“Sleep deprivation is usually not dangerous for the owner or rider. Horses do not suddenly collapse with this syndrome,” says Bertone. “However, in many cases they can be more problematic to handle, and some are aggressive towards other horses.”
He adds, “The impact of lack of sleep or even sleep deprivation on performance or how horses heal following injury is rarely considered, which is difficult to understand considering the importance of sleep in other species has been well-documented.”
Letting Sleeping Horses Lie
Over the past 20 years Bertone has collected data on nearly 400 horses with sleep deprivation behavior—a number that’s growing daily through digital consultation. Using this information he has developed a list of various causes of excessive drowsiness associated with lack of recumbent (lying down) sleep.
The top five potential reasons he says horses either refuse or are unable to lie down to sleep include:
Pain “If the process of lying down and/or standing is painful, then the horse is unlikely to voluntarily choose recumbent sleep,” says Bertone.
Musculoskeletal pain, such as osteoarthritis or abdominal or thoracic pain, might cause a horse to resist recumbency. Bertone recalls the case he was attending in his residency at Colorado State University in 1986 that sparked his interest in equine sleep patterns. A 12-year-old Quarter Horse gelding presented with severe weight loss that had developed over the preceding six months. Bertone noted 2-centimeter hairless calluses over the front of both forelimb fetlocks. During the horse’s three days of hospitalization, Bertone and colleagues noticed that when resting, the horse’s head reached within inches of the ground. The horse began to collapse, and the front of his fetlocks folded forward and hit the ground, explaining how the calluses formed. Ultimately, the horse was diagnosed with intestinal enteroliths (stones). During surgery the veterinarian found and removed extensive scar tissue and enteroliths from the abdominal cavity. One hour after returning to his stall, the horse lay down for the next 12 hours, and clinicians observed no further signs of collapse. Over the next few weeks the calluses disappeared.
Bertone’s interest was piqued because veterinarians frequently diagnose this type of behavior as “narcolepsy,” but narcolepsy neither resolves on its own nor disappears following changes to management, housing, herd dynamics, or pain medication.
Similarly, “narcolepsy is an extremely rare disorder in human sleep patients with most sleep physicians never seeing a live patient in an entire career,” says Bertone.
In his review of the literature and his experience collaborating with human sleep physicians, Bertone determined that this behavior and its response to management is not narcolepsy as has been previously ascribed in veterinary literature and defined by work in human medicine.
“I theorized that the adhesions between the large colon and the diaphragm made it very painful for the horse to lie down and to rise,” he explains. “The horse was therefore deficient in recumbent sleep.”
Neil Hudson, MA, VetMB, PhD, DEIM, Dipl. VetClinStud, MRCVS, senior lecturer at the University of Edinburgh Royal Dick Vet School, who has also completed equine sleep research, has listed other diagnoses to consider if your horse shows signs of sleep deprivation:
- Syncope (fainting);
- Seizures or epilepsy;
- Motor (muscular) paralysis;
- Hyperkalemic periodic paralysis (HYPP);
- Physical trauma;
- Myasthenic syndromes (disorders involving a problem at the nerve/muscle junction);
- Hypoglycemia (e.g., secondary to neoplasia, or tumors);
- Electrolyte abnormalities (e.g., hypocalcemia, hypokalemia, hyperkalemia);
- Endotoxemia; and
- Anaphylaxis (a rapidly developing, exaggerated allergic reaction).
In 2010 British researchers studied 25 horses evaluated for acute episodes of collapse. They made a final diagnosis in only 11 cases, and causes for collapse included:
- Cardiac arrhythmia (four horses);
- Right-sided heart failure (one horse);
- Hypoglycemia, or low blood sugar (two horses);
- Generalized seizures (two horses); and
- Sleep disorder (two horses).
Stacey Oke, DVM, MSc
Environmental insecurity Horses typically will not lie down if they are not “comfortable” with their surroundings. Bertone has observed this in many cases, particularly in horses that are not in a herd or do not have reliable vigilant horses protecting them while lying down.
Wohr and Erhard support this theory, adding that there is an ongoing discussion/debate about the implications of stabling horses individually versus in groups on sleep patterns.
“The lack of relaxation of the horses as a flight animal is an argument often put forward against individual housing. … In a natural herd lying positions are only assumed if one or more members watch over the herd,” they explain.
Bertone has successfully managed many horses with this problem using the following techniques:
- Adding a companion horse;
- Moving the horse to an area with more horses in the same confine;
- Removing an aggressive horse from an area, particularly if several horses in the group are affected with a sleep deprivation behavior;
- Increasing the stall or paddock size; and
- Moving the horse away from noise such as highways or high voltage power lines.
Dominance displacement Bertone says some horses, usually geldings, behave as the dominant horse in a group. This is similar to what many horse owners identify as aggressive geldings. Bertone theorizes that these horses do not rest because they must keep vigil on the herd. This condition most commonly occurs either when the entire herd contains geldings or when there is no alpha mare.
“An alpha horse (usually a mare) may fix the problem,” says Bertone.
Monotony “The best example I can give of this cause of excessive drowsiness is a horse restrained in cross-ties that is being braided,” Bertone explains. “The horse lowers its head until the point of near collapse, presumably because he is entering slow-wave sleep. It’s like being at the beach—they just get relaxed.”
Bertone warns that some of these horses might exhibit more exacerbated signs that take them out of the monotony group.
“Not all horses that (almost collapse) in cross-ties are just bored,” he says. “Standing in cross-ties is submission to authority. Many of the dominance displacement horses will have collapsing behavior in cross-ties, but they also have aggression moodiness, weight loss, and other signs that put them into (the) dominance displacement category.”
Sleep terrors “This is new,” says Bertone. “In the last year, several owners have sent me video of horses that exhibit the same behavior as human adults diagnosed with sleep terrors. These horses also present with sleep deprivation collapse. They lie on their side, have leg motions as if they are running, then rise in clear fear and confusion and remain agitated for many minutes. They repeat this over and over again.”
Bertone says he is working with several owners and veterinarians around the world to identify management approaches that might help horses with this issue.
Besides analgesics for routine pain relief, he’s prescribed drugs to manage sleep disorders in very few cases. “These drugs are not without risk; finding an environmental solution is a far better solution,” he adds.
There is no clear explanation for why sleep is necessary in horses (or any species), but researchers have determined that both environmental and physical factors can impact how much sleep an animal gets and, in some cases, a lack of sleep can be detrimental.
“An understanding of normal sleep behavior, positions, and acknowledgement that sleep deprivation and narcolepsy exists in horses will enhance the field of equine veterinary medicine by facilitating successful diagnostic and treatment plans for affected horses,” concludes Bertone.
About the Author
Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.
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