But horses have different characteristics from other domestic animals and like to sleep standing up at night. Whenever I go to see it at night, it always sleeps standing with its eyes closed.
The horse sleeps standing up and inherits the life habits of wild horses. Wild horses live in the endless desert grassland area. In ancient times, they were not only the hunting targets of human beings, but also the delicious home cooking of carnivores such as jackals. Unlike cattle and sheep, it can fight enemies with horns for a long time. The only way is to escape from the enemy. Jackals, wolves and other carnivores are nocturnal. They rest in hidden bushes or caves in soil and rocks during the day and come out to hunt at night. In order to escape from the enemy quickly and in time, wild horses dare not lie down and sleep at night. Even during the day, it has to stand and take a nap, keeping a high degree of vigilance to prevent accidents. Although the horses in the racecourse don't suffer from natural enemies and man-made injuries like wild horses, they are domesticated by wild horses, so the habit of sleeping standing up by wild horses is still preserved.
Besides horses, donkeys also have the habit of sleeping standing up, because their ancestors' living environment is very similar to that of wild horses.