In order to fully relax, the horse needs a few hours of REM sleep every night. In REM sleep, all muscles are completely relaxed. Amber Matthews, MSc, equine lecturer at Hartpury University, in Gloucestershire, UK, has investigated the influence of the amount of bedding in the stables on REM sleep. 

For the study, 6 different horses (stabled on wood shavings) with an average age of 15 years were observed. The horses were kept in their usual stable from 7:00 pm where they were monitored during the night (until 7:00 am) by means of infrared cameras. Time was also recorded when they were lying fully flat, lying sternally recumbent with or without their nose down, and sleeping standing up. Half of the horses started the experiment on 5 centimetre deep bedding for five nights, and the other half started five nights with 15 centimetre deep bedding. Then, after five days back on their standard bedding, all six horses switched to the opposite experimental bedding for five nights. 

Research showed that the horses spent significantly more time in REM sleep – as well as non-REM sleep – in the deeper bedding. Stabling horses on deeper bedding could therefore improve sleep quality. 

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