how an adulte horse rolling - video explainer

How the Adult Horse Sleeps
Mature horses most frequently rest in a standing position, but this does not provide deep, or REM, sleep. In order to fall into a true deep sleep, all skeletal muscles must be relaxed; this cannot happen when the horse is standing. However, when standing, horses will fall into a deep doze, but can wake up and become alert very quickly. This is a survival mechanism for horses, since they evolved as a prey species. But how can a horse snooze while standing? Horses have a unique anatomical mechanism in their hind legs called the stay apparatus. This allows a horse's knee cap to pop out of place and lock the hind limb in a standing position. Although it sounds painful, in horses, it's no problem at all. When dozing while standing, this stay apparatus will lock in place in only one hind leg; the other hind limb will be relaxed. Often, the horse appears to be leaning on one hip.

Most horses will lie down for deep sleep a few times each night, if they have a comfortable place to do so and feel safe. This is why it's important to provide a dry, sheltered area like a run-in shed or roomy stall, so your horse can stretch out safely for a snooze.