The Bloke On Who Wants To Be A...
Film, Media & TV1 min ago
No best answer has yet been selected by bkiseredward. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.Just to back Andy up a bit, horses do prefer to sleep standing up as it is their natural instinct to be able to escape at short notice. Horses will only really lie down if they feel secure.
Although a lot of horses lie down (mine included) it should be noted that if they lie down for too long then fluid can build up in their lungs and cause complications if the animal is already ill. Their sheer weight is just to much. So if a horse lies down for TOO long, then there is likely to be a problem.
Going back to my security thing, horses normally will only lie down OUTSIDE on a day when they can hear properly (hot days and frosty days) - if your horse lies down for any great period on a wet day or a windy day, it might be worth checking on them.