Why don’t horses sit or lie down even while sleeping?

Horses have an amazing ability to be able to sleep standing up. But they do also sleep lying down. If you’re a horse, you need to be able to do both.

Why don’t horses sit or lie down even while sleeping?A question from Zulfiqar

It's one of the mistakes lots of people make about horses. It’s true they do have an amazing ability to sleep standing up. But they do also sleep lying down. If you’re a horse, you need to be able to do both.

Animal behaviour expert Dr Susan Hazel explains why.

Horses have evolved to be able to run at almost any moment, in case a predator arrives. Flickr/Cowboy Dave CC BY-ND 2.0

Horses have evolved to be able to run at almost any moment, in case a predator arrives.
Flickr/Cowboy Dave CC BY-ND 2.0

Why should horses be able to sleep standing up?

Horses first evolved in open plains. As a prey species (one that other animals eat), they needed to be able to see quickly if another animal that might eat them (a predator) was nearby.

Being able to rest or sleep standing up meant they could get their rest, but if they saw a predator, they could quickly run away. That’s one of the reasons horses run so fast - to get away. The early horses that ran the fastest were more likely to survive.

Three legs on, one leg off

Horses can rest standing up or lying down. Flickr/Cowboy Dave, CC BY-ND 2.0

Horses can rest standing up or lying down.
Flickr/Cowboy Dave
CC BY-ND 2.0

The most interesting part of horses resting standing up is how they do it. In horses there is a special arrangement of muscles and the parts that connect muscles and bones together (ligaments and tendons). This is called the stay apparatus.

The stay apparatus means that horses can stand on three legs and rest the other leg. They can change the leg they rest so all of their legs get a chance to have a break. A horse can weigh more than 500kg so their legs need a rest!

Even though they can sleep standing up, scientists think horses still need to lie down and sleep each day. Your sleep is not the same all night. Everyone goes through different stages of lighter and deeper sleep, and horses are the same.

The deeper stages of sleep are only seen in horses lying down. Both horses and humans need to go through deeper stages of sleep for our brains to work properly.

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Tagged in School of Animal and Veterinary Sciences News, Animal Science News