The Dangers of Sleep Deprivation in Horses

Sleep is essential for life. The quality and quantity of a horse’s sleep directly affects their health and well-being. However, sleep is rarely considered as part of a horse’s management plan. A new study has found that poor management or physical problems can lead to horses becoming sleep deprived and at risk of serious injury.

Study highlights:

• Horses that don’t lie down sufficiently suffer from sleep deprivation leading to collapses.
• A 24-hour sleep laboratory monitoring study of 36 horses showed between four and 199 instances of collapse during the time period.
• Horses that collapsed had an altered and very restless sleep-profile. Their REM sleep phases were shorter and occurred while they were standing and, in 86 percent of cases, happened during, or immediately before the collapse.
• The number of collapses depended significantly on how much the horse had laid down in that time period and horses that did lie down showed significantly fewer collapses.
• Over 90 percent of the horses that collapsed were injured at some point.
• More research is needed to identify the factors that encourage recumbent sleep and prevent sleep deprivation.
• Sleep deprivation should not be confused with narcolepsy, which is a very rare chronic neurological disorder.

Sleep is a naturally occurring state involving both the body and the mind. While there is still a lot to be learned about the complex function of sleep, it is performed by almost every species and is vital for the performance and well-being of an individual.

Physiologically, during sleep, the individual enters a state of temporary unconsciousness and their muscles become inactive and relaxed. In the behavioural sense, the animal will seek a sheltered environment, adopt a certain posture, and stop responding to external stimuli.

There are three stages of physiological sleep and horses can achieve stages one (light sleep) and two (slow wave or deep sleep) while standing up. However, the third stage – rapid eye movement (REM) sleep – occurs only while the horse is lying down due to the complete muscle relaxation required. Previous research has shown horses can achieve REM sleep in both sternal (with their head supported on the floor) and lateral recumbency.

Horses in stables have been shown to have a regular total sleep time of three and a half hours per night. The duration of the different sleep stages is relatively constant. REM sleep totals about 30 minutes a night or 15 percent of the total sleep time, and slow-wave sleep takes up the most time at 65 percent. The rest of the total sleep time is spent in light sleep.