The Dangers of Sleep Deprivation in Horses

If horses don’t lie down for any reason, REM sleep deficiency (recumbent sleep deprivation) occurs. As a result, horses may fall into REM-sleep while standing, which consequently causes them to collapse due to the associated muscle relaxation. These collapses can cause severe injuries.

To find subjects for the study, the research team recruited owners whose horses had shown signs of collapsing. A detailed online questionnaire was completed by 177 respondents who were readers of a German equestrian magazine.

The research team visited 36 horses with collapses in their home environment and seven healthy, control-group horses. Each horse had a clinical examination, was observed for 24 hours and their management, stabling conditions, and medical histories were documented.

Each horse was also fitted with a mobile sleep laboratory to take polysomnographic readings for the 24-hour period. Polysomnography is a diagnostic tool that measures physiological functions during sleep. It simultaneously measures several body functions such as brain activity (electroencephalogram or EEG), eye movements (electrooculogram or EOG), and muscle tone (electromyogram or EMG), with which the depth and quality of sleep can be determined.

The online questionnaire showed a significant correlation between a change in the horse’s management or environment and their first collapses.

A third of the horses visited did not have enough space, according to the German guidelines for box stall dimensions.

In half of the horses visited, the onset of collapses was directly related to an event – a management change for example, a change of stable or a physical condition, such orthopaedic problems.

Over 90 percent of the horses studied showed injuries after collapsing. Injuries were mostly seen in the knees (72.4 percent) and the fetlocks (68.4 percent). Furthermore, 31.0 percent of the horses had head injuries and 18.4 percent had injuries to the hocks.

The examined horses collapsed a minimum of four and a maximum of 199 times during the 24-hour observation period. The individual number of collapses depended significantly on how much that horse had laid down.