Interestingly horse's can sleep both laying down and standing up. Although the type and length of these sleeping periods do vary depending on if our horse's are stood or laid down.
Our horse's like use have a sleep cycle containing different stages of sleep each with their own purpose. REM, light and deep sleep stages appear in both our own and our horse's sleep. But unlike us horse's don’t always go through all stages each time they sleep.
This is because horse's sleep for much shorter periods of time than we do. Usually only a hour or so at a time.
Deep sleep is key to our horse's health and ensures they feel rested and full of energy, however, horses will only go into a full deep sleep when they are laid down. Now, this isn’t usually a problem for horse's who have a safe place to lay.
However, some horse's will reduce the length of time they lay down. This can be for a variety of reasons:
Pain on laying or standing
Arthritis or old age preventing them from being able to lay comfortably
Not having what they deem as a safe place to lay
Injury or illness
Being alone- horse's will often only lay down when there is another trusted horse around
So what happens when our horses lay down less? In short, they don’t get enough deep sleep leaving them tired, lacking energy and vulnerable to illness and injury. But luckily they’re not completely without sleep as horses can also sleep standing up. But how do they do this? Using the reciprocal mechanism! So what is the reciprocal mechanism? The reciprocal mechanism also known as the stay apparatus is a mechanism by which horse's ensure their stifle and hock move together and allow them to lock out their stifle keeping them standing even when asleep. The only problem here being that our horse's can only sustain a short light period of sleep whilst stood upright. Other problems can also arise due to this mechanism most noticeably locking stifle also known as upward fixation of the patella. Upward fixation of the patella usually occurs in younger horse's but can also happen to older horses too. In younger horse's this occurs due to lack of strength in the quadriceps muscle. To lock out the stifle such as for sleeping a horse must hook the quadriceps tendons and associated ligaments over a notch in the femur. In young horse's the quadriceps muscle is often not yet strong enough to unhook these tendons leaving the stifle and hock locked in extension giving the characteristic dragging of the leg gait. In older horse's there can be reduced quad strength leading to locking stifle but older horses can also experience degeneration of the associated tendons and ligaments which can also leave them unable or unwilling due to pain to lock their stifle out and unlock it effectively. This can be troublesome if these horses are also struggling to lay down to sleep as then their ability to sleep is drastically reduced. So our horse's need at least a combination of these 2 methods of sleeping to live a happy healthy life ensuring they get enough deep, REM and light sleep.