How do horses sleep?

Rebecca Watson, advises what happens if a horse does not get enough sleep

Sleep is like money, if you have enough you don’t tend to worry about it. But if you are caught short, it can haunt your every waking minute. To an extent, the same is true for your horse.

First of all, let us bust the commonly believed myth that horses sleep standing up. Horses do rest standing up, they are even capable of short-wave sleep (SWS), but in order to achieve ‘proper’ sleep, they need to lie down.

The four stages of sleep

Awake

The horse is fully conscious and aware of his surroundings.

Dozing

The horse may doze in between episodes of eating. Stabled horses tend to spend less time eating than horses in a paddock, therefore have more time to doze.

The common stance of the dozing horse; lowered head position (below the withers) eyes half closed, ears and lips relaxed. Often standing on three legs, resting the fourth. The ‘stay apparatus’, which locks the joints in the limbs, allowing the horse to relax his muscles and doze in this stance.

Slow wave sleep (SWS)

SWS earns its name from the reduced electroencephalograph (EEG) patterns in the brain, which have been used to distinguish true sleep from waking. Although brain waves have been found to be similar in the dozing horse, it is believed that SWS is the first true stage of sleep that a sleeping animal must go through in order to reach deeper, REM sleep. Horses in SWS are able to use their stay apparatus to remain standing, however, they will often lie down in sternal recumbency, balancing on the sternum with their legs tucked under them.

Rapid Eye Movement sleep (REM)

REM is also called paradoxical sleep due to the similarities in the brain waves to that of the waking animal. EEG patterns suggest that the mind is as active as when the horse is awake, but in reality, REM sleep is deeper than SWS. During REM sleep the heart beats slightly faster, but the respiratory rate decreases, the body is completely relaxed with a complete loss of muscle tone. The horse will be fully recumbent, stretched out on his side. Just as with humans, REM sleep in horses results in involuntary twitching of the muscles of the eyes, lips and limbs. This is unquestionably the most important part of sleep and although not fully understood, it is believed to be partly responsible for both the physical and mental wellbeing of all animals.

How does the horse sleep?

The ‘stay apparatus’ allows the horse to rest while standing up; the stay apparatus is a group of ligaments, tendons and muscles that brace the joints of both the forelegs and the hind legs. The stifles have a locking mechanism that enables one leg to lock in place, whilst the other one rests. This clever adaptation allows the horse to snooze whilst standing, but react quickly to danger and flee from predators in the wild.

While the horse is not necessarily nocturnal (night active) or diurnal (day active), they have alternating cycles of foraging or eating and resting during a twenty-four hour period. The duration of activity will be influenced by environmental and seasonal factors, such as temperature and the availability of food. Biologists use the term ‘cathemeral’ to describe species like the horse that are neither nocturnal nor diurnal in their activity and sleeping patterns.

Most domestic stabled horses will sleep between midnight and 4am, this is largely because of the diurnal cycle of the humans taking care of them. Horses turned out 24/7 will display round the clock intermittent foraging and resting, just as they would in the wild.

Sleep studies in horses demonstrate that they do not have long periods of uninterrupted sleep, like us humans. On average, horses sleep for a total of three to five hours in a twenty-four-hour period; this will comprise of a total of approximately three hours of SWS and less than an hour of REM, in four to five sleep periods. Typically, the REM sleep usually occurs as numerous five-minute periods.

Sleep patterns change with age; young foals lie down for frequent naps between feeds and tend to spend almost half their day asleep, as the foal ages naps become less frequent. Younger horses (<2yo) have been found to spend longer lying down sleeping than adult horses. Senior horses, just like some senior people, tend to doze more frequently. Wild horses tend to sleep less than domestic counterparts, this is mostly due to the availability of food. Wild horses need to roam foraging for nourishment, sometimes travelling great distances, preferring to pause for sleep during the hottest time of the day. For this reason horses can actually go without REM sleep for days, but there comes a time when the body has to catch up and rest properly.

A horse will not lie down to sleep if he does not feel safe or secure. Both horses in the wild and groups of horses at pasture will often have one or two ‘sentries’ on duty whilst the majority of the herd lie down to sleep. These horses will rest standing up, to keep an eye out for any possible danger. New surroundings or pain can prevent horses from lying down; if a horse does not think he can get up quickly (and escape) he will not lie down to sleep.

We naturally think that horses should feel safer in a barn or a stable; whilst most horses acclimatise to their environment, not all horses feel secure in an enclosed space. Many will not lie down inside, preferring to sleep in the paddock – where scary predators cannot sneak up on them so easily! Interestingly, studies have found that horses prefer to lie down on harder ground.

In sleep studies horses always chose the hard ground over soft bedding. Perhaps this is because having secure footing beneath them makes them feel better able to flee, should the need arise. Horses that are deprived of good quality REM sleep over a long period of time, just as with people, can be susceptible not only to ill health, but to temperament problems and neuroses. A sleep deprived horse will often appear to ‘drift off’ into a deep sleep whilst standing and apparently buckle over at the knees as his body responds to total relaxation of the muscles, ligaments and tendons. As he begins to fall, he awakens abruptly before he falls over.

 

Sleep deprivation

This occurs because horses either do not have time to lie down or, they simply refuse to for various reasons:

Pain: Horses avoid lying down due to physical pain associated with lying down or getting back up. Most commonly due to musculoskeletal pain, although thoracic (in the case of pneumonia) or abdominal pain (peritonitis or late gestation) can also play a role. In some cases, vets can manage these cases with analgesia.

Fear

Horses are uncomfortable in their environment. This insecurity is likely to stem from the horse’s prey / herd instinct. Management strategies to combat this behaviour include:

• Adding another horse or companion to the stable or paddock
• Removing a potentially aggressive horse from the herd
• Removing the affected horse from areas near loud, ‘threatening’ noises
• Increasing the stable size or leaving th horse in the paddock

Dominance displacement

This most commonly affects geldings that try to control a herd lacking a dominant mare. These horses are often seen as aggressive towards others. Sleep deprivation becomes evident when the horse is removed from the herd or stabled; they do not rest as they must keep vigil on the herd.Sleep deprivation is not usually dangerous for horse and rider, but affected horses can become hard to handle and aggressive towards other equines. Sleep deprivation behaviours can usually be managed, however, what works for one horse may not work for another. Sometimes behavioural cases have very subtle causes of sleep deprivation and often are overlooked, i.e. a horse wearing (or not wearing) a rug, field geography or weather conditions.

Sleep deprivation can be misdiagnosed as narcolepsy (a condition of the brain characterised by falling asleep over and over) however, narcolepsy neither resolves on its own nor disappears due to environmental or management changes. The impact of lack of sleep on performance or, how horses heal following an injury or a surgery is rarely considered.

When travelling to competitions, where it is necessary to stay overnight, it is recommended to stick to your horse’s normal daily routine as much as possible, to prevent disrupting the horse’s sleep pattern. The strange environment can be un-nerving and sleep can be difficult for the horse, like people, all horses are different – some will adapt to a strange bed and lie down to sleep no problem, others will find it hard to relax away from home.

Bear in mind if you are nervous about the situation, your horse will likely pick up on this, making a good nights’ sleep harder to attain!It can be un-nerving and sleep can be difficult in a strange environment, like people, all horses are different. Some will adapt to a strange bed and lie down to sleep no problem, others will find it hard to relax away from home. Bear in mind if you are nervous about the situation, your horse will likely pick up on this!