Towards an objective measurement of sleep quality in non-human animals; using the horse as a model species for the creation of sleep quality indices.

Sleep disturbance is observed across species, resulting in neurocognitive dysfunction and poor impulse control/regulation of negative emotion. Understanding animal sleep disturbance is thus important to understand how environmental factors influence animal sleep and day-to-day welfare. Self-reporting tools for sleep disturbance are commonly used in human research to determine sleep quality, that cannot be transferred to non-verbal animal species research. Human research has, however, successfully used frequency of awakenings to create an objective measurement of sleep quality. The aim of this study was to utilise a novel sleep quality scoring system for a non-human mammalian species. Five separate sleep quality indices calculations were developed using frequency of awakenings and total sleep time/total time spent in different sleep states. These indices were applied to a pre-existing data set of equine sleep behaviour taken from a study investigating the effects of environmental change (lighting and bedding) on the duration of time in different sleep states. Significant treatment effects for index scores both differed and aligned to the original sleep quantity results, thus sleep quality may be a useful alternative measurement of sleep disturbance that could be used to investigate impactful (emotional, cognitive) effects on the animal.