A chronically sleep-deprived horse cycles between arousing and lying down. | Photo Courtesy Dr. Joseph J. Bertone

Little is known about equine sleep patterns, but they appear to take several forms.

Sleep, patterns of sleep, and sleep behavior are, in general, not major areas of concern for equine veterinarians. However, many practitioners have seen cases of sleep disorders and have found few resources on diagnostic approaches and treatment protocols. In this article we’ll look at what we do know.

First, let’s dismiss the idea that horses get a full range of sleep while standing. Recumbent sleep (while lying down) is essential for a horse’s well-being. Horses usually require 15 minutes of recumbent paradoxical sleep (when rapid eye movement occurs) daily but, unlike many other species, they can put off this 15 minutes for prolonged periods. Historical data indicates that horses can experience recumbent sleep deprivation for two weeks before they begin to show classic clinical signs of it: partial collapse with recovery, or getting back on their feet. 

Second, most cases of sleep deprivation behavior have been labeled as narcolepsy. However, if you look at comparative literature, likely what we are seeing in horses is not narcolepsy. In fact, the tests often used to diagnose narcolepsy in horses—the physostigmine challenge used to induce narcolepsy in dogs or testing cerebrospinal fluid for the neuropeptide hypocretin, for ­instance—are unlikely to work in horses. In addition, many sleep deprivation cases respond well to management changes that impact behavior, as well as to pain medications. Narcolepsy would respond to neither