Sleep deprivation occurs in horses that have not received the required daily 30 to 60 minutes of Rapid Eye Movement (REM) sleep for a week or more. When horses are not able to lie down and enter REM sleep to refresh themselves, they may experience "sleep attacks." That is, during quiet periods they enter the first two stages of sleep -deep restfulness and slow wave- before progressing to the REM stage and partially collapsing. In sleep deprivation, horses become drowsy before falling completely asleep, which may cause their legs to buckle.
There can be physical and psychological reasons for sleep deprivation in horses. Physical reasons include the inability to lie down which may be environment-related (eg stall size) but may also be due to pain or restricted movement. For example, an older horse with arthritis in his knees or ankles may not be able to get down or back up. Psychological reasons include feeling too insecure to lie down on the ground long enough to enter REM sleep because there is no herdmate on guard. The removal of a dominant, older mare from an established herd is an example of this cause of sleep deprivation.
Narcolepsy is different than sleep deprivation. According to equine neurologist Steven Reed, DVM, ACVIM, narcolepsy can be defined as a rare and incurable sleep disorder of the central nervous system characterized by uncontrolled episodes of loss of muscle tone (cataplexy) and sleep. Any horse that appears drowsy, weak or collapses should be examined by a veterinarian for an accurate diagnosis since this type of medical condition can be dangerous to both the horse and his handler.
SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.