2.2. Behavioural observations
Eighteen sows and their litters were video recorded on Day 1 (from the end of farrowing until 24 h pp) and Day 3 (48–72 h pp). For each pen, one camera (Sony HD 1080; HD-SR 12), attached to a tripod, was positioned so sow and piglet behaviour in the pen could be recorded. A microphone, positioned 1.4 m above the floor in the middle of the sow area, was connected via cables to the camera.
2.2.1. Analysis of the sow pre-lying communication
Video analysis of sow pre-lying communication started 2 min before a sow began to lie down and the following behaviours were recorded during these 2 min: the frequency of vocalization, the frequency of sniffing and the frequency of nudging. Sow pre-lying communication was calculated based on the total frequencies of pre-lying behaviours occurring during that event (for definitions see Table 1a). We analyzed 10 standing-to-lying events per sow without external disturbance on Day 1 and on Day 3. Some sows had less than 10 standing-to-lying down events per day without external disturbance (11 sows on Day 1 (mean ± SD: 5 ± 2.2) and 12 sows on Day 3 (mean ± SD: 7.5 ± 3.8)). Altogether 125 standing-to-lying down events were analyzed on Day 1 and 135 on Day 3. As a result of technical difficulties it was not possible to analyze the grunting vocalization in 25 standing-to-lying down events.