Sessions

Pig production for pork consumption has increased globally, accompanied by an intensification of production systems. Improving animal welfare remains an important challenge in intensive pig production. As pigs cannot verbally communicate their welfare state, reliable and objective physiological indicators are needed for welfare assessment. In recent years, heart rate variability (HRV) has proven to be a valuable physiological parameter for assessing stress and welfare in farm animals. A major advantage of HRV is that it can be measured non-invasively and continuously. However, obtaining high-quality electrocardiogram (ECG) recordings with minimal artefacts in awake, unrestrained adult sows (Sus scrofa domesticus) remains challenging, particularly because of movement-related artefacts. Therefore, this study aimed to develop and refine a non-invasive fixation method for reliable long-term ECG recordings and subsequent HRV analysis. The fixation method was progressively adapted until it remained stable in place for approximately 24 hours and was well tolerated by the sows. During the official study phase, 18 recording sessions were performed in 15 animals using the Bittium Faros 180L; 17 of them yielded ECG data, and three sows were recorded twice. Device-reported signal quality was higher after the introduction of electrode gel (median 83.75% vs 60.7%). From 14 sows, ten consecutive 5-min segments per recording were taken from the predefined 23:00-05:00 time window and analysed with Kubios HRV Scientific 4.3.0 for time-domain and non-linear parameters. Of the 140 segments, 125 (89.3%) met the predefined quality criteria (at most 5% corrected beats and no excessive noise or heavy ectopy on visual ECG review). The first three qualifying segments of each sow were used for the HRV evaluation. Nine sows showed a sinus-like rhythm (median RMSSD 40.7 ms). In four sows, an irregular rhythm, labelled as atrial fibrillation by the device software but not confirmed, produced very high RMSSD values that do not reflect vagal tone.One sow, which had a mammary abscess, showed arrhythmias, a high heart rate and very low HRV and is described separately as a case observation.These findings indicate that the developed fixation method enables non-invasive, long-term ECG recording suitable for HRV analysis in awake, unrestrained adult sows, provided that the analysed segments are also reviewed visually, and may provide a methodological basis for future studies.