The effect of group-housing with free-farrowing pens on reproductive traits and the behaviour of low-risk and high-risk crushing sows

Free-farrowing systems and group-housing systems for lactating sows are sensitive systems and require an optimal interaction of different environmental factors to be successful. The aim of the present study was to compare sows' reproductive traits during lactation in two group-housing systems (GH; GH(big): n = 40; GH(small): n = 40) and in a single-housing system (SH; n = 63). The two GH systems differed in size (GH(big): 8.3 m(2) / sow; 7.1 m(2) / sow). The GH sows were separated into free-farrowing pens from three days ante partum until six days post partum. For the remaining time, the sows and piglets were allowed to run together in the whole GH system. Data were collected in four batches with 20 GH sows (GH(big): n = 10; GH(small): n = 10) and 16 SH sows in each housing system. Regarding the reproductive traits, sows of both GH systems had significantly more total piglet losses (e.g. crushing, underweight, runt) and crushed more piglets during lactation compared to the SH sows (p < 0.05). In addition, the GH(small) sows had higher total piglet losses and crushed more piglets compared to the GHbig sows (p < 0.05). Besides the reproductive traits, the lying down and rolling behaviour of both high risk crushing sows (HRC; >= 35% crushed piglets; n = 10) and low-risk crushing sows (LRC; <= 20% crushed piglets; n = 10) in the GH system were investigated in the first 72 h post partum to obtain more information about critical situations of piglets being crushed. HRC and LRC sows did not differ in their frequency of lying down movements, However, HRC and LRC sows performed more lying down movements by using the pen walls, which has been described as the safest way to prevent crushing. With regard to rolling movements, HRC sows rolled more frequently and performed significantly more 180 degrees rolling movements from one side to the other side (p < 0.05) and 90 degrees rolling movements 'onto belly' from the side onto the belly (p < 0.05). Furthermore, piglets of HRC sows were significantly less active during postural changes (p < 0.05). In conclusion, the safety of the piglets with regard to higher pre-weaning mortality was reduced in the GH systems with the free-farrowing pens. In addition, the pen size of the free-farrowing pens of the GH systems had an influence on the total piglet losses. More piglet losses were documented for sows in smaller free-farrowing pens. Additionally, the detailed observation of HRC and LRC sows within the same housing system showed high variation in their maternal behaviour and in their postural changes in free-farrowing pens. Especially HRC sows performed more rolling movements compared to LRC sows.