A lot of people think that when a horse lies down it means he’s ill. Truth is, he may just be enjoying a good sleep!
What ’s normal?
Regular sleep patterns in horses vary considerably depending on a variety of factors including environmental conditions, feed, pain, age, companionship and time of day. There are two types of sleep.
1. Rapid eye movement (REM) sleep
This is the kind of deep sleep that allows you to dream. We don’t know if animals dream, but they do twitch, “run” and vocalize while in REM sleep.
To truly differentiate REM sleep from SWS sleep (see next page), it’s necessary to measure the brain waves with an electroencephalogram or EEG. REM sleep is most similar to wakefulness in its EEG – fast and irregular. During REM, most of the muscles are inactive (atonic), except those of the face and legs. The eye muscles contract frequently, which is where the term “rapid eye movement” comes from.
Horses must lie down for REM sleep. They will either lie on their sides or sternal (chest) with their noses on the ground. During REM sleep, horses will exhibit an increased heart rate, decreased respiratory rate and leg movements. They will typically go through very short (five minute) periods of REM sleep for up to about 45 minutes to an hour. They will REM sleep daily to every few days, and according to some sources need about two hours of REM sleep weekly. Young horses sleep more often and have more REM sleep than adults.
Horses in a stable will spend an average of two hours a day recumbent, but broken up into four to five time periods. If that same horse is turned out to a new pasture, however, he will not lie down for at least one night, and will generally sleep less for about a month.
If a horse is deprived of REM sleep for several weeks, however, his behavior begins to change. He’ll be more likely to spook, exhibit distracted behavior, rest his muzzle on a feeder or fence, and buckle at the knees.
2. Slow wave sleep (SWS)
This kind of sleep is identified on an EEG by slow, regular waves. During SWS, a horse can remain standing by utilizing the stay apparatus in his legs. This system of tendons and ligaments locks the legs without requiring active muscle participation, allowing the flight muscles to rest. This adaptation probably arose from the wild horse’s need to flee when danger approached.
A horse that snoozes while standing will have a lowered head and neck. His eyes will be closed, his ears back, and he’ll often have one hind leg cocked. This allows him to take naps frequently through the day and night without lying down.
Horses only spend about two hours a day in SWS. During the daylight hours, they are awake and alert 88% of the time. At night, they are awake as much as 71% of the time, with 19% of the night spent in a drowsy state.
Equine sleep disorders
Narcolepsy is a sleep disorder seen infrequently in horses. The signs are similar to those of a sleep-deprived horse, but happen even without the deprivation. It is characterized by excessive sleepiness with uncontrollable sleep attacks. Cataplexy, a sudden loss of muscle control while conscious, is seen in horses with narcolepsy.
There are two narcoleptic syndromes in the horse.
1. The first is seen within a few days of birth, and may improve over time. There have been reports of neonatal (and likely familial) narcolepsy in miniature horses, warmbloods, Shetland ponies, fell ponies and Suffolk horses. Episodes in these foals may be induced by stimulation such as feeding or grooming. The foals remain affected but severity, frequency and duration can decrease over time.
2. The other form occurs in mature horses. Narcolepsy in adult horses may be true narcolepsy with cataplexy, or idiopathic hypersomnia (meaning the cause of excessive sleeping is unknown), which is not true narcolepsy.
A wide range of breeds and crosses have been affected with narcolepsy, and there is no set age at which it may begin. Symptoms can range from hanging the head and neck and buckling at the knees, to sudden collapse. Horses can experience lacerations to their muzzle, inner lip (from hitting their teeth), carpus and fetlocks. These attacks can occur as frequently as ten times a day to once every few weeks.
If the horse is walked during an attack, he may look ataxic (uncoordinated). There have even been reports of narcolepsy occurring while horses are being ridden, so obviously there is a hazard to both horse and rider. Some attacks can be induced by grooming, washing, saddling or walking the horse out of a stall.
Diagnosing the problem
If you suspect your horse may have narcolepsy, your veterinarian can perform some tests on him. There are some risks associated with administering drugs to induce a narcoleptic state, so be sure to talk to your vet about them. Obviously the horse should have a good clinical checkup, including a musculoskeletal exam, blood work and a thorough history. This is necessary to distinguish between sleep disorders, sleep deprivation problems, seizures and syncope or other disease processes. Therapeutic drugs are reported to help with narcolepsy.
Getting to know your horse’s sleeping patterns can tell you a lot about his comfort level and overall health. So next time you see him lying down in the pasture, don’t panic – he’s most likely just getting some shut-eye!
After discovering at an early age that she had a real connection with animals, Kim Sergent set her sights on Veterinary School. She graduated in 1989 from the University of California, Davis and began practicing equine veterinary medicine In the san diego area.
She began to discover health and behavioral problems which could not be treated Medically and sought an alternative, a more complete approach to veterinary care. In 1997 she was certified for Musculo-Skeletal Manipulation by the American Veterinary Chiropractic Association, and began to integrate chiropractics into Her veterinary practice. In 2002 she graduated from Colorado State University Veterinary Acupuncture School, and has more recently been studying herbology and homeopathy.
Dr. Sergent’s practice is based in Alpine and still services most of San Diego County. She is a member of the American Veterinary Medical Association, American Veterinary Chiropractic Association and the American Association of Wquine Practitioners. www.acequine.com