Page 155 - January_2023

VETERINARY VIEWS
SLEEP AND SLEEP DISORDERS IN HORSES
by Nancy S. Loving, DVM
Have you witnessed a horse asleep on its feet, catching itself just before it falls? Have you seen a drowsy horse fall to its knees or fetlocks? Unlike humans, adult horses average only about 3-5 hours of sleep per day, with sleep events occurring intermittently throughout the day and night in 15-minute
In humans, sleep is classified into
several stages: Stage 1 is the wake stage of drowsiness, Stage 2 is light sleep, Stage 3 and 4 are slow wave or delta sleep, and then there is REM (rapid eye movement) sleep which may include dreaming. Humans average 4 – 5 cycles of non-REM (stages 1 – 4) and REM
lying down in
sternal recumbency or standing in the drowsy stance but with the head dropped lower than the height of the withers. A
horse may remain standing to
segments, with most occurring at night. Lack of sleep or a sleep disorder has the potential to impact a horse’s physical activity, attitude, and quality of life. Horses experience sleep disorders
that can result in injury from falling.
It helps to know
what signs to look
for so you can relay information to your veterinarian to achieve the best protection and resolution.
during a full night’s sleep.
Because horses maintain a state of
vigilance hard-wired into them as a prey species, it is difficult to measure the transition from wakefulness to drowsiness using an encephalogram of the brain (EEG) and electromyogram of the muscles (EMG). Usually, the upright stance of a sleeping horse assumes full weight on both front legs and
a rear leg while the other rear leg is cocked
or “primed” to kick if necessary. Horse sleep stages 2-4 are referred to as slow wave sleep; these typically occur either with the horse
sleep if he is uncomfortable with the security of the environment or due to pain-related musculoskeletal problems.
A horse in REM sleep experiences rapid
eye movements and relaxed neck muscles. Some REM episodes include leg movements, twitching muscles and/or ears, blinking, and nostril flares. You have probably witnessed your horse displaying these movements while in deep sleep. For horses, only 15 % (30 minutes per day) of total sleep is REM stage. Usually, a horse lies flat out on the ground to reach REM sleep but can also experience REM sleep while in sternal recumbency. If a horse experiences REM sleep while standing, there is the possibility of partial collapsing episodes due to relaxed muscular tone.
Usually, a horse lies flat out on the ground to reach REM sleep but can also experience REM sleep while in sternal
recumbency.
Because horses maintain a state of vigilance hard-wired into them as a prey species, it is difficult to measure the transition from wakefulness to drowsiness using an encephalogram of the brain (EEG) and electromyogram of the muscles (EMG).
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