Let’s clear up a common misunderstanding about horses: they do not sleep standing up. They snooze standing up. There’s a big difference.
Horses, like humans and, in fact, all land mammals, require deep sleep for proper mental and physical functioning. But for a prey species like the horse, whose existence in the wild depends on its ability to outrun predators, deep sleep can be a serious threat to personal safety. So how do horses get enough sleep?
For starters, horses doze a lot. On any given day, drive past a pasture of horses and count how many are grazing and how many are just standing there, heads down, lower lips drooping. Those are your snoozers, standing up.
Horses are able to get some light shut-eye without lying down by way of a really cool aspect specific to equine anatomy called the stay apparatus. When a horse is standing at rest, he is able to lock his kneecap with ligaments and tendons keeping the joints in alignment. With these soft tissues locking the bones together, no extra exertion from muscle use is required. This allows the horse to actually rest while standing.
But what about that deep sleep I mentioned earlier? Horses can’t attain deep REM sleep by standing; this is only accomplished when the animal lies down. Therefore, horses do lie down to get proper sleep. They just don’t do it for very long.
It turns out that horses do not require a lot of REM sleep — roughly two to three hours a night, typically in short bursts of ten to twenty minutes at a time. A typical night as a horse will involve grazing, snoozing standing up, and short periods of lying flat out to get some serious shut eye.
The important thing to note is that horses will only lie down to sleep if they feel safe in their environment, because obviously this action is very risky if you’re a prey animal in a potentially threatening situation. This issue of environmental stress also affects domesticated horses. While usually not threatened by mountain lions or wolves or other predators when in a farm pasture or in a stall for the night, if the horse is stressed, he will not lay down to sleep.
Very busy, loud barns, or an area that is too small for the horse to feel comfortable lying down are some common problems for the modern horse. And the result? Horses that go without REM sleep over the course of weeks will have a negative effect on physical performance, and may even factor into irritability or behavioral problems. That’s right — everyone needs beauty sleep, not just us humans.
Dr. Anna O'Brien