Normally, horses will spend about 30 minutes a day in REM sleep. They may become sleep deprived if they are unable or unwilling to lie down – for example because of insecurity, or orthopaedic problems. Such horses may lapse into REM sleep while standing and then collapse.

Zsofia Kelemen and co-workers at the University of Veterinary Medicine Vienna conducted a study to investigate the effect of age and orthopaedic problems on the time spent lying down.  A report of the work is published in the journal Animals.

A total of eighty-three horses, ages ranging from two to 32 years old, with or without orthopaedic problems, were involved in the study.

The research team used wearable automated motion sensors to monitor the time the horses spent lying, moving, and standing. Horses were tracked continuously for 60-hour sessions. Horses with abnormal recumbency patterns were monitored more often and for longer.

Eight horses, all with chronic orthopaedic disease, showed signs of REM sleep deficit. They were either seen to collapse, or had abrasions over their knees presumed to be due to falling onto the knees. These horses spent significantly less time lying down.

However, in this study, neither age nor lameness due to chronic orthopaedic disease significantly influenced the time spent lying down.

The authors conclude that wearable sensor technology can be used to identify horses with low recumbency times at risk for REM sleep deficiency and to assess and monitor equine welfare objectively.

For more details, see: Recumbency as an Equine Welfare Indicator in Geriatric Horses and Horses with Chronic Orthopaedic Disease.
Kelemen Z, Grimm H, Long M, Auer U, Jenner F. Animals. 2021; 11(11):3189.
https://doi.org/10.3390/ani11113189

Press release by Mark Andrews - Equine Guelph February News