As humans, we sleep around one third of our entire life. For a long time, sleep was seen as a passive state during which only necessary bodily functions are active. It is only more recently that sleep has been understood as an “active behavioural state” instead of a “passive resting state” due to an increasing number of studies of the central nervous system and the associated characteristic functions going along with sleep. The importance of sleep for mental, physical, and psychological functionality is thus a relative recent area of research. In pigs, the conditions for sleep on farm are very far away from the conditions of pigs living in a natural environment. Improving our understanding of sleep may lead to changes in housing conditions and management procedures, thereby improving animal welfare.

Pigs spend around one third of their life asleep, but knowledge on how sleep quality and quantity affect pig welfare is scarce. Early studies in the 1970s used electrodes implanted into pigs’ skulls to obtain polysomnographic measurements, i.e. physiological recordings of sleep including electroencephalography (EEG). Only more recently have researchers started to investigate non-invasive self-adhesive electrodes to study sleep in pigs. However, this methodology is not only time-consuming, but also restricted to isolated pigs since conspecifics would otherwise explore and manipulate the electrodes. Since pigs live most of their lives in social groups, polysomnography cannot currently be used in farm settings.

The overall aim of our research on sleep in sows was 1) to establish a non-invasive polysomnographic recording method of sleep using electroencephalography (EEG); eye movements, which are measured using an electrooculogram (EOG); and muscle activity, which is recorded by an electromyogram (EMG) and 2) to use the polysomnographic measures to identify postures and subtle behaviours that allow differentiation of different sleep stages on a behavioural level. However, while the handling and the preparation of the sows (i.e. shaving, washing, sticking the electrodes, etc.) was much less problematic than we initially thought and the sows seemingly even enjoyed the practice, we faced technical problems with the polysomnographic device and artefacts in the recordings when electrodes loosened overnight. Despite a lot of time and effort invested in this project by the MSc student, we ended up with recordings of only six sows, which is not enough for a rigorous statistical analysis.

In a preliminary study, we collected polysomnographic measures of highly pregnant sows after they were isolated from the group for farrowing and recorded their behaviour at the same time. We faced unreliable recordings due to loosening of the electrodes overnight. Consequently, in the current study, we aimed to systematically investigate how to better fixate the electrodes. Based on this study, we suggest using electric clippers instead of a razor to shave the sows. Moreover, our study revealed that extra gel placed on the electrodes greatly improved the signal and that fixating electrodes and cables with kinesiology tape helps keeping both in place. This project lays the foundation for non-invasive polysomnographic recordings to identify postures and behaviours that can be used to identify different sleep stages in sows. If successful, these behavioural indicators can then be applied in future studies to gain insight into different factors affecting pig sleep and, consequently, pig welfare, thereby paving the ground for future research shedding light on a highly important – though so far neglected – part of pigs’ lives.