- 2-Hour Guided Primitive Trail Ride for One with Meal
How Horses Sleep Standing Up: Four-Legged Minutemen
If you’re curious about what your ride does after you give it a goodbye pat, check out Groupon’s explanation of how horses sleep on their feet.
They can weigh up to a ton. Their heads can look down from a height of 6 feet. Their legs, in proportion, seem downright scrawny. And yet horses spend about 80% of their lives standing up, including periods of sleep lasting four hours at a stretch. The secret to this feat of endurance is in a special arrangement of bones, tendons, and ligaments called the passive stay apparatus. The unique interlocking of the joints in each leg shifts much of the horse’s weight from the muscles, which tire over time, to the connective tissues, which don’t. In the hind legs, the knee joints themselves can shift into a locked position that keeps them stable enough to give one rear leg a few hours off at a time.
This system stops working during REM sleep, which horses—like humans—need in addition to lighter slow-wave sleep. During REM, the brain shuts off neurons in parts of the spinal cord like lights in an unused wing of a building, paralyzing the limbs. Since some muscle tone is still needed to keep a horse upright, going into REM sleep while standing would cause the horse to collapse. Accordingly, most horses lie down for at least 30 minutes a day.
Why not catch all their Z_s while stretched out in the paddock or the pasture? That’s likely _because horses are so big. For one thing, many of their bones are quite fragile in comparison to their bulk, so lying down for long periods puts stress on body parts that aren’t designed to take it. The second factor is a matter not just of health but also of survival. Standing up is a relatively laborious process for a horse, which makes it more vulnerable than smaller animals when lying down in the wild. Accordingly, the hypothesis goes, horses’ legs evolved their locking mechanism to allow a swifter getaway when they sense the presence of a predator or a 4-year-old who wants to braid their mane.