Standing horses retained muscle tone during a state resembling rapid-eye-movement (REM) sleep, while the complete pattern appeared in animals lying down. A single peer-reviewed study followed eight healthy mares, pairing brain signals with video and other physiological measurements. The findings complicate the use of posture to assess equine sleep; each animal contributed only one analysed cycle.
Rapid eye movements accompanied two distinct physiological states in eight healthy mares. Animals sleeping on their feet kept enough muscle activity to remain upright; those lying down displayed the full rapid-eye-movement, or REM, pattern. Both chest-resting and side-lying horses could enter REM. The same visible position also accompanied other stages, complicating estimates of sleep quality based solely on time spent in a particular posture.[1]
Researchers combined electroencephalography, the measurement of brain electrical activity, with synchronized video and signals from eyes and muscles. The healthy adult Mangalarga mares came from a university teaching and research herd. All had lain down in a preliminary observation, but during the instrumented recordings four remained upright and four lay down. Light sleep occupied most of the cycles selected for analysis.[1]
This single peer-reviewed descriptive investigation analysed one complete cycle from each horse. Posture groups arose from the animals’ own behaviour, and one investigator assessed the traces without blinding. Those features and the small sample restrict comparisons across horses and management conditions. Continuous monitoring over a full day was absent. The authors call for standardized electrode placement and sleep scoring to make future equine measurements more comparable.[1]
