Abstract
In human sleep studies, the probability of discomfort from the electrodes and the change in environment usually results in first-night recordings being discarded. Sleep recordings from the first night in human subjects often differ in amount of REM (rapid eye movement) sleep and the overall sleep architecture. This study investigated whether recordings of sleep states in dairy cows also show a first-night effect. Non-invasive electrophysiological recordings were carried out on nine cows of the Swedish Red breed during three consecutive 24-hour periods (recording days 1–3). Overall, cows spent 12.9 ± 1.4 hours awake, 8.2 ± 1 hours ruminating, 57.2 ± 20.3 min drowsing, 44.1 ± 20.2 min in REM sleep and 64.3 ± 38.1 min in NREM (non-rapid eye movement) sleep (mean ± SD) and there were no significant differences between recording days in total duration for any of the sleep and awake states. However, the bouts of REM sleep and rumination were longer, and the awake bouts were shorter, at night time compared to daytime, regardless of recording day. The awake bouts also showed an interaction effect with longer bouts at daytime during day 1 compared to daytime on day 3. Data on sleep and awake states recorded in adult dairy cows during three consecutive 24-h periods showed great variation in sleep time between cows, but total time for each state was not significantly affected by recording day. Further and more detailed studies of how sleep architecture is affected by recording day is necessary to fully comprehend the first-night effect in dairy cows.
Highlights
Modern research on sleep relies on non-invasive recordings of the electrophysiology of the brain, commonly using skin adhesive electrodes
Both rapid eye movement (REM) sleep bouts and rumination bouts were longer during night compared to daytime, but there were no differences between recording days and no interaction effect of recording day × time of day
The percentage of non-rapid eye movement (NREM) sleep bouts were higher at night compared to daytime (P < 0.001; Table 3), but there were no effect of time of the day or recording day
Summary
Modern research on sleep relies on non-invasive recordings of the electrophysiology of the brain, commonly using skin adhesive electrodes. Work by Rechtschaffen and Verdone [1] showed that total sleep time did not differ between recording nights, but rapid eye movement (REM) sleep decreased and number of awakenings increased in human subjects during the first night compared with the fourth night of recording in a sleep laboratory. When estimating average total lying time in dairy cows on herd level, accuracy changed little between the 3- and 5-day sampling period [6]
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