Nursing synchronisation in lactating sows as affected by activity, distance between the sows and playback of nursing vocalisations

In this study, the amount of nursing synchronisation was quantified, the dependence of the degree of synchronisation on the spatial distance between sows was examined, and the effect of nursing vocalisation playback on nursing frequency and nursing synchronisation was assessed in a large commercial pig farm. Sows were housed in individual farrowing crates, 14 sows per room. Twelve rooms were assigned to one of four treatments in a 2x2 experimental design, with the factors being AGE of piglets (observations at either 6-10 days or at 13-17 days post partum) and BASS frequencies on the loudspeakers being switched on or off. The third factor (PLAYBACK) was applied in a repeated measures design on the 3 days of observation in each room. Three-min playbacks of sow nursing sounds were played back every 45, or 55 min, or not at all, for a period of 24 h on the 3 days. The nursing behaviour and its synchronisation were recorded in two ways: through a 2 h direct interval sampling observations of all sows and through a 6 h video recording of three focal sows. The nursing synchronisation, measured in standardized degree of synchrony (SDS, i.e. proportion maximally possible synchronisation), was high at 0.53. This SDS in nursing was much higher than the SDS in activity which only reached 0.26. Synchronisation in pairs of sows declined with increasing distance. A significant quadratic effect in this relationship indicated that the decline was steepest when pairs of sows housed in neighbouring pens and pairs of sows one crate away were compared. The playback of nursing sounds did not increase either the nursing frequency or the nursing synchronisation. It is concluded that nursing synchronisation is high in large rooms with crated sows, that it is not a sole consequence of synchronisation in general activity, that it depends on the distance between the sows, and that an increase in nursing frequency is not always reliably induced by a playback of pig nursing vocalisations..