"Sleep is one of the most relevant behaviors for biological functioning." All animals must sleep. Sleep deprivation in horses negatively impacts immune system function, and impairs memory, learning, and physical performance. Research in other species has shown that sleep deprivation can lead to mood swings, hallucinations, and even death. Horses can sleep lightly while standing, thanks in part to the stay apparatus, but they must lie down each day to achieve a minimum of 30 minutes of REM sleep. This phase of the sleep cycle is characterized by rapid eye movement and an absence of muscular tone, and it cannot be achieved while standing. Sleep deprivation in horses is a serious health and welfare issue, and horses won't lie down to sleep for a number of reasons, such as:
when they don't feel safe to do so
if lying down is painful or difficult
if they aren't provided with suitable locations or materials upon which to lie down
Horses in herds take turns sleeping, and they may feel lying down to sleep is unsafe if they are socially isolated or in small groups. They may also feel unsafe if housed with incompatible horses. Feeling unsafe can also occur when horses are transported to new or unfamiliar locations, such as show grounds or a new boarding facility. Lying down may be painful for horses with untreated medical conditions such as arthritis. For geriatric horses with decreased muscle mass it may be physically difficult for them to lower themselves to the ground and rise again. This can leave geriatric horses feeling insecure in their ability to get up quickly if required.
What type of space do horses need in order to get a good night's sleep?
Horses need a suitable space to sleep. It should be an appropriate distance from obstacles such as walls or fences. It should be dry, and preferably be of a soft material which conforms to the horse's body. It should also be large enough, which can be a problem in some types of horse management systems - whether single stalls or group housing.
Recent research (1) from Switzerland looked at the role substrate and size of sleeping area had on horses. It was discovered that the presence or absence of a soft substrate (e.g. straw or shavings) in group housing situations, and the area of that available substrate had an effect on lying down behavior. Horses who had no bedding - only rubber mats - rarely lay down, and if they did it was for less than 30 minutes at a time. Horses would lie down on rubber mats if no bedding was available, but would choose bedded areas (and not lie on rubber mats) when given the choice. Available space to sleep may be a resource in short-supply for domesticated horses kept in group-living systems. The researchers found that lower ranking horses would rise prematurely from sleep if there was minimal bedded space available, but would stay sleeping longer when that area's size was increased. Larger bedded areas were more appealing to horses, as shown by the length of time they achieved REM sleep.
Signs of sleep deprivation in horses
Visible signs of sleep deprivation in horses can include excessive drowsiness, followed by buckling of the front limbs resulting in the horse almost collapsing to the ground. This is often misdiagnosed as narcolepsy, but true narcolepsy in horses is very rare. Owners may not always witness collapsing behavior, and instead may notice frequent, unexplained scuffing of the horse's front legs or joints. In stalled horses, a lack of bedding in the mane and tail may indicate the horse is not lying down to sleep and sleep patterns should be monitored.
Whether you house your horse individually or in a group-housing setting, consideration should be given to the size of the available sleeping space, the substrate upon which the horses will lie, and how safe all of the horses feel in that space. If you are concerned that your horse isn't sleeping enough, here's a few things to consider that may improve your horse's ability to sleep:
have your veterinarian rule out pain or other physical reasons your horse may be reluctant to lie down
evaluate both the available substrate and size of the area available for sleeping
observe the relationships between the horses who are neighbors or who share space, to determine if there is any bullying or other reasons to cause your horse to feel anxious about lying down
On-going sleep deprivation is a serious health and welfare issue for horses. If you are unable to determine and correct the cause for your horse's sleep deprivation, contact a horse behavior consultant for further help.