This is fascinating!
I just was reading an article online the other day about horses and sleep and a little on the research that is being done at the University of Pennsylvania's Equine Clinic.
Sue McDonnell, the head of the Clinic, had some interesting insights;
Feral horses tend to sleep more than stabled horses, and tend to hand off sentinel duty (so Annie, Storm is definitely handing the baton to you!)
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I also thought this was interesting:
<<Even though they're able to snooze standing, horses apparently need to lie down for rest and sleep at least some of the time. In fact, scientists think horses must lie down to go into deep stages of sleep. Like humans and many other animals, horses experience both slow-wave sleep (SWS) and rapid-eye-movement (REM) deep sleep. (SWS is characterized by slow, synchronized waves of electrical activity in the brain as recorded by electroencephalography. REM sleep is characterized by jerky eye movements and rapid, disorganized brain waves.) REM sleep seems to occur mostly when the horse is stretched out flat on his side, rather than resting on his chest.
People dream during REM sleep, and it seems that horses do, too. Beneath closed lids, their eyes move rapidly back and forth. Sue McDonnell has even seen some horses move their feet as if "trotting" in their dreams. But what horses dream about is anyone's guess.>>
This is from
http://www.all-creatures.org/nyca/ch-art-20000900.html