It's a widely held misconception that horses aren't affected by sleep deprivation. Most require at least four hours of slumber, including about 60 minutes of rapid eye movement (REM) sleep, during a 24-hour period. If a horse misses out on sleep for several days, he can become so exhausted that he literally falls asleep on his feet, collapsing.
Sleep deprivation is often confused with narcolepsy, a rare neurological disorder that produces excessive sleepiness, but it is usually much easier to remedy. Take the following steps to ensure your horse gets sufficient sleep each day:
Turn off the lights. Horses who are used to falling asleep outside in the darkness may have trouble snoozing if they're moved to brightly lit stalls. They can eventually adapt to brighter conditions---broodmares kept under artificial light for extended periods of time show few adverse effects---but they will be sleepy until they do.
Provide ample bedding. REM sleep can be achieved only when the horse is lying flat out or in sternal recumbency with his nose resting on the ground. You can encourage your horse to get off his feet by making the floor more comfortable. In one study, horses were more likely to lie down in a stall deeply bedded with shavings.
Keep it quiet. Horses are light snoozers, so at night try to keep the barn quiet or provide "white noise," such as easy-listening music turned down low.
Stable horses in congenial groups. Horses tend to sleep better when surrounded by other horses, but only if they all get along. Make sure your horse is friendly with herdmates in adjoining stalls. If two horses bicker all night, they may keep the whole barn awake.