Domestic horses are domesticated by wild horses. It inherits the living habits of wild horses by sleeping standing. Animals living in complex natural environment have specific sleeping posture, which is their sleeping habit formed in the fierce competition for survival in nature.
Wild horses are herbivores living on the grassland. They are often threatened by predators and are in danger of being eaten at any time. Therefore, they never lie down, but stand with their heads raised and their eyes closed as in the daytime. This sleeping posture has the functions of defending against enemies, convenient escape, timely warning and ensuring safety. After a horse runs around, when he stands in the shade to rest, he can “doze” once by lowering his head and closing his eyes.