Lying posture does not accurately indicate sleep stage in dairy cows

Quality sleep is important for physical health and welfare in animals. However, we know little about dairy cow sleep, and how much they need. Practical techniques are needed to monitor sleep in cows to determine how different management practices affect their sleep and their welfare. It is impractical to use ‘gold standard’ electrophysiological - polysomnography (PSG) to identify sleep in cows. Previous work suggests lying postures are useful to identify sleep stages in calves, but the reliability of lying behaviour to identify these sleep stages in adult cows is uncertain. We compared the lying postures of adult dairy cows (deep bedded on straw or in a pasture) with PSG, to determine if lying postures could be used to accurately identify rapid eye movement (REM) and the different stages of non-REM (NREM) sleep. Lying in the typical “sleep” posture with the head turned and resting on the flank identified approximately 70% of REM sleep in outdoor managed cows but was less accurate in indoor housed cows that showed REM sleep in numerous postures. Lying with the head still and low did not identify stages of NREM sleep in either group. Using the tucked ‘sleep posture’ to estimate total sleep would be an over estimation of REM sleep, but also an underestimation of total sleep as this posture would omit most NREM sleep. Lying postures are not useful indicators of sleep stages in dairy cows and additional research is required to identify efficacious alternative techniques.