The Effects of Mild Disturbances on Sleep Behaviour in Laying Hens

SIMPLE SUMMARY: Farm animal welfare is important to both farmers and consumers. Sleep behaviour may offer an additional means of assessing welfare at night, where our understanding is comparatively poor. However, our present understanding of sleep in poultry is lacking. The objectives of this study were to establish a baseline for undisturbed sleep behaviour in laying hens and to then apply brief disturbances (wind, noise and light for 5 min every 30 min) and observe the subsequent effects. Sleep during lights off was comprised of two states: slow-wave sleep (SWS) and rapid eye movement (REM) sleep. Over all the types of nights, SWS constituted 58% of nighttime behaviour, and REM sleep constituted 18%, with the remaining 24% attributed to being awake. The disturbances were effective at waking laying hens when applied but had no significant carry over effects on the distributions of sleep and wakefulness behaviours into the day or next night. The patterning of sleep behaviour in laying hens is similar to other avian species, including the presence of some degree of resilience to sleep disturbances. These results further improve our understanding of this behaviour in laying hens and suggest that these short-term disturbances can be adequately compensated for within the same period shortly following disturbance. ABSTRACT: The positive welfare of commercial animals presents many benefits, making the accurate assessment of welfare important. Assessments frequently use behaviour to determine welfare state; however, nighttime behaviours are often ignored. Sleep behaviour may offer new insights into welfare assessments. This study aimed to establish a baseline for sleep behaviour in laying hens and to then apply mild short-term disturbances and observe the subsequent effects. Twelve laying hens were divided into four batches and were surgically implanted with electroencephalogram (EEG) devices to record their brain activity. The batches were subjected to undisturbed, disturbed and recovery types of nights. Disturbed nights consisted of systematic sequences of disturbance application (wind, 90 dB noise or 20 lux light) applied one at a time for 5 min every 30 min from 21:00 to 03:00 (lights off period: 19:00–05:00). Sleep state was scored using EEG data and behaviour data from infrared cameras. Over all the types of night hens engaged in both SWS (58%) and REM sleep (18%) during lights off. When applied, the disturbances were effective at altering the amounts of wakefulness and SWS (Time × Type of Night, p < 0.001, p = 0.017, respectively), whereas REM sleep was unaltered (p = 0.540). There was no evidence of carry-over effects over the following day or night. Laying hens may be resilient to short-term sleep disruption by compensating for this in the same night, suggesting that these disturbances do not impact their long-term welfare (i.e., over days). Sleep behaviour potentially offers a unique means of assessing an aspect of animal welfare that, to date, has been poorly studied.