I follow a few different "horse-y" groups on Facebook, and lately I've noticed an interesting trend: people posting videos of their horses spontaneously falling so deeply asleep standing up that they fall down in their stalls. Nine times out of ten, the poster is asking for veterinary advice because they believe their horse has narcolepsy.
Now, I'm not a veterinarian and so cannot diagnose these individual horses. However, I firmly believe that we can begin to theorize why this phenomenon happens if we take a closer look at the natural sleep behaviors of the horse.
About the Equine Sleep Cycle
There are two types of true sleep in horses: slow-wave sleep (SWS) and rapid eye movement (REM) sleep, which together form a sleep cycle. While horses do drowse in a standing position for about 2 hours per day (you can recognize it by how they stand with their head dropped and one back hoof cocked up), they need both slow-wave and REM sleep in order to form the proper sleep cycles to be fully rested.
Slow-wave sleep can occur when a horse is standing or while lying down in sternal recumbency (lying down with chest upright), but REM sleep only occurs while a horse is lying completely down on its side, in a position known as lateral recumbency. Altogether, adult horses sleep like this about 3 to 5 hours per day, generally between 8:00 pm and 5:00 pm, as well as between noon and 2:00 pm.
Because the equine sleep cycle relies upon the horse's ability to lie down, it follows that a horse's ability to achieve full sleep also relies upon a horse's sense of security (other horses standing sentry in case of predators, for example) and physical comfort in lying down.
How Can We Use This Information to Understand Sleep Issues with Our Horses?
Knowing these facts, it stands to reason that horses can easily become sleep-deprived if they aren't able to comfortably lie down. And, like in the video examples I've seen online, sleep deprivation can lead to suddenly falling deeply asleep standing up, in what looks like an episode of narcolepsy.
So what are the factors that can lead to this sleep deprivation? For stalled horses, this can occur if their stall is too small for them to comfortably lie down in, if their bedding is not deep enough, or if there is a change in the stable environment that makes them feel too insecure to fully fall asleep. For pastured horses, there may be a perceived threat nearby, or perhaps the lack of companionship of another horse to stand sentry impacts the horse's sense of security in lying down. It's important to look at all the factors of the horse's daily life: is a scheduled riding lesson interrupting the time of day that the horse tends to sleep, for example?
As always, if you have concerns about your horse's health, it's best to consult a veterinarian. However, understanding the natural sleep needs and patterns of horses serves as a good baseline for managing your own horse's well-being and perhaps seeing where some things can be tweaked to their benefit.
Sources and Recommended Reading:
Most of my data and information has been sourced from Equine Behavior: A Guide for Veterinarians and Equine Scientists (Second Edition) by Paul McGreevy. I highly recommend it for a more in-depth explanation of equine sleep patterns.
>> I get commissions for purchases made through links in this post. <<