Effects of space allowance on the welfare of dry sows kept in dynamic groups and fed with an electronic sow feeder

The minimal legal space allowance for grouped pregnant sows in the EU is 2.25 m(2)/sow. The effect of higher space per animal on agonistic behaviour and social stress of animals living in dynamic groups is not known.
Two groups of 34 pregnant Belgian Landrace sows were housed in two pens of respectively 102 m(2) (3 m(2)/sow) and 76.5 m(2) (2.25 m(2)/sow). Each sow lived there for 15 weeks. Sows were fed through an electronic sow feeder. According to the dynamic system, one third of each group (i.e. 11 or 12 nearly parturient sows) was replaced every 5 weeks by the same number of recently inseminated sows. Welfare indicators were collected during six of these 5 week-periods: performance, agonistic behaviour, skin lesion score and salivary cortisol. No differences were observed for production parameters, or for fighting activity. However, the mean number of one-way aggressions, when observed during 2 h-periods at 3 and 8 days after grouping, was significantly lower in the large pen than in the small one (respectively 16 +/- 2 versus 26 +/- 3, p < 0.01, and 10 +/- 2 versus 20 +/- 5, p < 0.05). The mean number of injuries was also lower with the 3 m(2) space allowance, when collected on the introduced sows one, 2 and 3 weeks after grouping. Some contradictory differences in salivary cortisol were noted 2 and 26 h after mixing, but without reaching statistical significance. An available area 33% higher than the EU legal minimum reduced agonistic behaviour and consecutive wounds and thus induced better welfare conditions for sows living in dynamic groups and fed with an electronic sow feeder. The impact on productivity and social physiological stress need further research.