In group-farrowing systems, piglets usually mingle into large groups of 50–100 at about 10 days of age with the presence of their mother. At weaning, sows are removed and piglets remain in the same group until 8–9 weeks then they are transferred to new accommodations for finishing (Li et al., 2010 and Olsen et al., 1998). The possible advantage of group-farrowing systems to pigs includes being exposed to a large area and complicated environment, and interacting with other conspecifics (Hillmann et al., 2003). In addition, pigs reared in group-farrowing systems are weaned in their large home pen which can alleviate weaning stress associated with mixing and moving (Hessel et al., 2006).