This is a very common question among people regarding large animals like horses and cows sleeping while standing up.

Horses can only lie down for short periods of time because their heart will stop if they lie down for too long. Yup, you read that correctly, horses will die if they lay down for too long. Why is this?

This is because the horse’s cardiovascular system runs all the way down their legs and into the soles of their hooves. By standing and applying pressure on these points, horses keep the blood flowing in their body. If the horse were to lay down for too long, blood would no longer pump to its heart causing it to do so.

So, when horses are standing, blood actively flows through all four hooves.