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Dr. Joe Bertone from the Western University Veterinary School in California, has provided some very useful and important information about sleep depravation (Excessive Drowsiness) in the horse.

As a vet, I have frequently been asked about horses that appear to just collapse while standing in the field. Some horses seem to just fall asleep in cross ties. Others have been noted to almost fall down while been tacked up or being lead out to the riding ring. Some classic signs that very often indicate a problem with sleep depravation are scrapes or calluses appearing on the front of the front limb fetlock or knee joints. If you think about the way a horse normally gets up or down it is virtually impossible for these lesions to develop as abrasions from flooring or bedding. They are caused by a horse buckling or falling and tearing the skin on the ground or barn floor.

There are 3 categories of Excessive Drowsiness or Sleep Depravation identified by Dr Bertone.

1. "Pain associated Excessive Drowsiness is defined as those cases where horses do not lie down because it is painful to do so, or it is painful to rise or both. Most often these horses have musculoskeletal issues that create pain or mechanical difficulties on attempts at recumbency or rising to stand. In addition, horses have episodes of excessive sleepiness in association with thoracic or abdominal pain that is elicited with recumbency or on attempting to stand.
2. Environmental insecurity associated Excessive Drowsiness, is the condition where horses do not lie down because they are psychologically uncomfortable doing so, because horses will only lie down when they are environmentally comfortable. One can assume that this stems from horses as prey and also herd behavior. The author has managed several horses with this syndrome by adding a friend to the pasture or stall, or moving the horse to an area where there are more horses, or removing an aggressive horse from a group where several horses may have the problem. This would also include horses in an insecure environment that may just require a larger stall or paddock, or those horses near loud harassing noise, like fireworks, or speedways.
3. Monotony induced Excessive Drowsiness is best exemplified by the horse in crossties being braided that begins to lower its head to the point of near collapse. This is assumed to be the horse moving from slow wave to paradoxical sleep. This may also be seen more commonly at the odd hours that owners tend to braid horses. The horse is often very comfortable in its environment and near sleep is simply induced.”

Sleep depravation, if recognized, has traditionally been diagnosed as equine narcolepsy. This condition, although diagnosed in the horse is an extremely rare condition. It is highly unlikely that horses presenting with signs of sleep depravation have narcolepsy.
Although the physiology of horse sleep is not completely understood it is known that in order for a horse to complete its sleep cycle it needs to sleep at least a couple of hours a day lying down. It becomes clearer why horses with chronic or acutely painful conditions will have sleep related issues. I have now on several occasions diagnosed arthritic conditions which when addressed have alleviated the sleep depravation and those nasty chronic skin lesions on the fetlock. There are many fascinating behavioral aspects of sleep depravation. When the behavior of horses in a herd environment are examined, it becomes easier to understand why certain horses kept in a small group or perhaps in a stable may develop sleep related issues. Modifying the social interactions of your horses may help alleviate sleep depravation problems. When horse showing remember that situations where all night noise or activity preventing sleep can lead to performance problems. Come to think of it this is a condition which might well apply equally to the horses and their riders!
For more in-depth information on this condition you can contact our office for Dr. Bertone’s paper on this interesting topic.