Sleep Deprivation vs. NarcolepsyRegular deep sleep is as important to the horse as it is to a human being. The average horse will devote approximately 3-5 hours per day to sleep. Contrary to popular belief, a horse will lie down for a period of deep sleep. However, if this period of deep sleep is avoided for a significant period of time, excessive drowsiness and periodic collapse can occur as a result. These horses are often thought to have narcolepsy, a sleep disorder causing abrupt onset of “sleep attacks”. Narcolepsy has been described in the horse, but is exceedingly rare and typically breed associated. More on narcolepsy later…it is much more likely that these horses are simply suffering from sleep deprivation.
Owners will often complain of unexplained “rub” sores on the knees and fetlocks, periodic episodes of collapse, falling asleep during grooming with subsequent collapse. They may also present with abrasions to the nose and head as a result of hitting the ground or other objects. There are a number of different reasons that sleep deprivation can occur. They include both physical and environmental factors.
Physical factors run the gamut from cardiovascular and respiratory abnormalities to neurologic disorders and metabolic derangements. A thorough physical exam and requisite blood work is warranted to help rule out any of these types of problems. Pain can also be a cause for excessive wakefulness. Musculoskeletal pain may prevent a horse from being able to lie down or get up resulting in a lack of deep sleep. In these cases a short course of analgesics may result in an improved ability to get up and down.
Environmental factors may prevent sleep in a number of different ways. For example, a dominant horse may not sleep enough as a result of being constantly on alert for threats, conversely, a horse that is lower in the pecking order may not sleep enough if he is constantly harassed by his herd mates. Lone horses may also suffer sleep deprivation if they feel too vulnerable to sleep deeply. Excessive noise and a lack of adequate bedding can also contribute to sleep deprivation. Environmental changes such as separating or moving certain individuals, providing a friend (such as a goat or another horse), providing deeper bedding and eliminating noisy disruptions can allow the affected individual to get some rest resulting in an alleviation of clinical signs.
Now, the brief story on narcolepsy; narcolepsy is a sleep disorder in which the affected individual has below normal levels of a hormone called hypocretin. It is usually associated with cataplexy – loss of motor control and preceded by a period of excitement. This excitement is usually positive, such as that associated with playing or feeding time. There is a strong familial association of the disorder in miniature horses. It does occur in horses, but it is extremely rare.
If you feel that your horse is suffering from sleep deprivation or narcolepsy it may be helpful in diagnosis to videotape your horse in his normal environment for 24-48 hours. Determine whether these episodes are preceded by external stimuli such as playing or feeding time. Take a look around the paddock to identify sources of excessive noise or disruption. If you have multiple horses determine whether the affected horse is dominant or submissive. All this information will help your veterinarian in formulating an accurate diagnosis. He will also want to perform a full physical exam and possibly blood work to help rule-out concurrent illness.