Чому коні й корови іноді сплять стоячи? | Why do horses and cows sometimes sleep standing up?

Horses and cows can doze and sleep while standing, using mechanisms that help support their legs with little muscular effort. But this does not replace all sleep: rapid eye movement, or REM, sleep generally requires lying down, when the muscles are relaxed. So the animals need a safe, comfortable place where they can lie down.