Many causes contribute to sleep disorders in horses

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Pain or physical discomfort. Lyme disease. Environmental insecurity. Monotony. Aggression issues. Sleep terrors.

These are among the possible causes contributing to sleep disorders in horses, said Dr. Joseph J. Bertone, professor of equine medicine at the Western University of Health Sciences College of Veterinary Medicine.

Dr. Bertone presented “Sleep Disorders in Horses: A Review and Classification of 420 Cases” at the June forum of the American College of Veterinary Internal Medicine in Denver. Afterward, he spoke with JAVMA News about the subject, which has been an interest of his throughout his career.

He saw his first case three decades ago when he was a resident working toward becoming an ACVIM diplomate in large animal internal medicine. A horse with severe weight loss came in for a workup and kept collapsing in the stall. The veterinarians found and removed a staple that had migrated from the colon into the diaphragm and two enteroliths. The horse was in good condition at a recheck three months later.

The scars on the dorsal surface of the fetlock joints of both forelimbs in this horse resulted from the horse collapsing because of sleep deprivation. (Courtesy of Dr. Joseph J. Bertone)

Dr. Bertone thought about the case and concluded that the horse could not lie down comfortably to sleep because the colon had become adhered to the diaphragm. He said, “There’s a misconception that horses can have the full range of sleep while standing, and that’s not true.” Horses can have certain cycles of sleep standing, but they cannot normally enter the paradoxical sleep phase in which rapid eye movement occurs. 

He subsequently evaluated similar cases of collapsing behavior and sleep deprivation in horses, and he had collected 445 as of mid-June. The ACVIM session covered 420 cases from 2000-2016.

“The commonality is the secondary behavior, which is sleep-deprivation behavior,” he said. He also has found that although many cases relate to pain or physical discomfort, most are behavioral in origin.

In each case, he starts by asking whether the horse can lie down and roll comfortably. If not, sources of pain or physical discomfort might include severe joint disease, polysaccharide storage myopathy and many other musculoskeletal diseases, gastric ulcers, abdominal adhesions, or late pregnancy. In a few cases, sleep disorders have resolved with treatment for Lyme disease. Dr. Bertone noted that Lyme disease can cause pain.

On the behavioral side, environmental insecurity appears to be the most common cause of sleep disorders in horses. Environmental issues include changes in stall size, stall relocation, loss of other horses, changes in lighting, blanket issues, window coverings, and weather. Dr. Bertone has had several cases that he believes resulted from the noise of high-voltage power lines.

Some horses had signs of a sleep disorder only in association with monotony. When in cross-ties, for example, some horses begin to fall asleep, then collapse.

Another group of horses with sleep disorders is what laypersons refer to as aggressive geldings. These geldings seem to want to dominate the herd in the absence of a mare by trying to fulfill the position of the alpha mare and do not want to lie down. These cases are often resolved with the addition of an alpha mare.

In the past few years, Dr. Bertone also has identified horses with evidence of behavior similar to sleep terrors in human patients. This condition occurs before paradoxical sleep, so that phase is never achieved, and the horses have sleep-deprivation behavior.

Dealing with sleep disorders in horses can involve pain management, treatment for Lyme disease, environmental adjustments, adding an alpha mare, and other approaches. Some approaches to night terrors include environmental analysis, use of diazepam, late-night feeding, and use of melatonin.

Melatonin, tranquilizers, and other drugs also are an option in the many cases in which the cause of the sleep disorder is unclear. Trainers can also work on getting the horse to lie down.

Dr. Bertone said attendees at the ACVIM session showed much interest and asked many questions.