Equids -- specifically horses, donkeys and zebras -- are the only animals that sleep standing up, an evolutionary talent that allows them to doze and still be ready to flee from predators at a moment’s notice. Mature horses, for example, frequently rest standing up, aided by what’s known as the “stay apparatus” of the forelegs and the “check apparatus” of the hind legs. This anatomical system lets them snooze without falling down, with little or no muscular effort.
Of course, horses and other equids also lie down to get deeper REM sleep, and may even snore and twitch as though they are dreaming.
The sleeping habits of horses:
- Adult horses sleep for about three hours a day. The length and type of sleep depends on diet, temperature, activity level, gestation, and gender. Older horses doze more frequently.
- A horse’s sleeping pattern changes according to age. Foals lie down for frequent naps and sleep for half the day. As a foal gets older, they take fewer naps and are more likely to sleep upright.
- Lying down is actually quite stressful for a horse. Their weight puts pressure on the internal organs.