Sow and piglet behaviour in group lactation housing from 7 or 14 days postpartum

Under natural conditions, sows and piglets abandon the nest between 7 and 14 days postpartum and re-join the group. If given the choice, commercially housed sows begin to nurse piglets communally around this time. The best age at which to group sows and their litters in two-stage group lactation systems has not been determined. A total of 112 multiparous sows and their litters were allocated to three lactation housing treatments over four time replicates. All sows farrowed in standard farrowing crates. Group lactation (GL) sows were transferred to group pens (one pen of 5 sows at 8.4 m2/sow and one pen of 7 sows at 8.1 m2/sow, per GL treatment and replicate) with their litters at 7 (GL7; n = 48 sow and litter units) or 14 (GL14; n = 48 sow and litter units) days postpartum until weaning. Farrowing crate (FC; n = 16 sow and litter units) sows and their litters remained within FC in single litters until weaning. In each replicate, two focal sows per GL pen (one high and one low parity) were video recorded for 1 h post-mixing. The GL focal sows, along with 4 FC sows (two high and two low parity) and 2 focal piglets per focal sow (one average sized male and one average sized female), were also recorded from 0700 to 1700 on the day after mixing and 2 days before weaning. Data gathered continuously from video records included sow aggressive and nursing behaviours while sow and piglet time-budgets were observed using point sampling at 5-min intervals. Social affiliative nosing was more frequent between GL14 than GL7 sows (P = 0.01), but aggression did not differ (P > 0.05). There were no other effects of litter age at mixing on sow or piglet behaviour (P > 0.05). Compared to FC sows, GL sows were more active (P P P = 0.03). However, GL sows had fewer successful nursings (P = 0.002) and terminated more nursings (P = 0.001) than FC sows. The time GL piglets spent suckling (P P = 0.001) sows other than their dam increased over time. Compared to FC piglets, GL piglets spent more time in the creep (P = 0.05), active when outside of the creep (P = 0.04) and investigating the pen (P = 0.02), and less time manipulating other piglets (P = 0.005). There do not appear to be behavioural differences in sows and piglets between mixing into GL at 7 or 14 days postpartum. While GL allows for the expression of maternal and exploratory behaviours, these benefits come at the cost of disrupted nursing behaviour and cross-suckling