The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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14 TheHorse.com THE HORSE December 2017 AAEP FORUM JOSEPH J. BERTONE, DVM, MS, DIPL. ACVIM TheHorse.com/AAEP-Forum S leep, patterns of sleep, and sleep behavior are, in general, not major areas of concern for equine veteri- narians. 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 move- ment occurs) daily but, unlike many other species, they can put off this 15 minutes for prolonged periods. Historical data indicates that horses can experience re- cumbent 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 narco- lepsy. However, if you look at compara- tive 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 neu- ropeptide 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. Currently, based on historical infor- mation and response to therapy, there seem to be at least six categories of sleep deprivation in horses. 1. Pain or physical discomfort-associated This category includes horses that have been clearly diagnosed with pain- ful conditions ranging from severe joint disease, polysaccharide storage myopathy, and other musculoskeletal diseases to gastric ulcers, abdominal adhesions, and late pregnancy. It also includes cases that respond to non- specific pain management (such as non-steroidal anti-inflammatory drug administration for joint pain), omepra- zole for treating gastric ulcers, or birth in late- pregnancy mares, which invari- ably resolves the discomfort. 2. Environmental insecurity-associated This category includes horses whose clinical signs resolve after caretakers or veterinarians identify and change environmental issues. These include stall-size changes, stall relocation, loss of other horses to which the patient seemed be attached, light bulb wattage changes, blanket issues, window cover- ings, weather, and many more seeming- ly incidental environmental issues that, when addressed, lead to resolution. 3. Monotony-associated Horses in this group show signs only when placed in cross-ties long-term or forced to stand quietly for prolonged periods. These horses do not express this behavior at other times. Simple intermittent stimu- lation helps resolve the behavior. 4. Aggression displacement (aggressive gelding)-associated Horses that show excessive and continuous aggression toward one or all horses in a group fall into this category. These horses respond to the addition of an alpha female or, more rarely, an alpha male when available. 5. Lyme disease-associated Horses test- ing positive for Lyme disease without fitting under any other category are in this group. They do not show evidence of joint pain, and they respond to Lyme disease therapy. 6. Sleep terror-associated This category includes horses with behavior resem- bling sleep terror behavior in humans. This is a relatively new finding, with all cases identified since January 2012. As night videography capabilities become more inexpensive, we might see more of these cases. Horses that respond to the appropriate therapy gain weight, have better attitudes, become less aggressive toward other horses, perform better, etc. In the equine veterinary field there is a traditional lack of concern with horses' sleep and its impact on performance and its clinical outcome. Owners com- monly seek help outside of veterinary or university sources because few answers or expertise exist. This is difficult to under- stand in light of the need for sleep's essen- tial, sustaining, recuperative physiology. There is no definitive explanation for the necessity or function of sleep in horses, or for that matter in most other species in which the need for sleep varies widely. Likely, it is a complex of metabolic and adaptive needs developed and dependent on the niche each species fills in nature. h 6 Types of Sleep Deprivation in Horses Fetlock lesions can be indicative of sleep depri- vation. Here, a chronically sleep-deprived horse cycles between arousing and lying down. COURTESY DR. JOSEPH J. BERTONE American Association of Equine Practitioners, 4033 Iron Works Parkway, Lexington, KY 40511 • 859/233-0147 • www.aaep.org