Why do cows sleep standing up?
Cows and horses sometimes do sleep standing up. But, they do not always sleep while standing. If they lie down, their weight will press their lungs and does not allow the cow to breathe properly. It appears that the cow feels more comfortable to stand. Even if they lie down, they remain upright and just fold their legs. If they lie down on one side, they will be in trouble and may die due to lack of breathing.
Cows generally sit or lie down to chew whatever it has eaten sometime back. Cows lie down for chewing and for digesting the food they ate recently. They generally sleep for about 3 to 4 hours in a day. They spend more time for digesting their food by sitting rather for sleeping. Rarely cows sleep while standing. They sleep mostly when they sit down.
Animals which sleep while standing generally do that because they can escape very easily when there is any dangerous situation. The cows lie down to sleep when the animal feels safer. Otherwise it does not want to lie down for sleeping. They prefer relaxing or sleeping standing up as it will be difficult for them to get up rapidly and easily. When we see the structure of cow, it is so big with well built fat, muscles, other organs and four chambered stomach and so on. With this heavy built, it is highly difficult for the cow to sleep standing. Probably, it will be drowsy while standing. But, it will definitely take rest for long duration by lying on the ground.
If the cow is away from the herd, in order to protect itself and be watchful for its enemies they take a nap by standing. If they are in herds, they feel safer to take a nap while standing. Otherwise, they would prefer to sleep by lying down.