Does social competition affect the reproductive performance of sows moved to group housing after weaning?

This study was undertaken to examine the effects of grouping sows immediately after weaning or 4 weeks after insemination on i) the occurrence of skin injuries and ii) reproductive parameters such as weaning-to-service interval and pregnancy and culling rates. At weaning (T0), 106 sows were allocated to multiple group housing (MG, n = 41) or to individual stalls (CG, n = 65). Sows from CG remained in individual stalls until 28 days after service, in compliance with the Council Directive 2008/120/EC, and were then mixed into static groups. The occurrence, localization and severity of skin injuries and lameness were recorded 24 h after allocation (T1) and 7 days later (T2). Sows were artificially inseminated on natural estrus, between T1 and T2. At T1, 20 of 41 (49%) sows in MG displayed cutaneous lesions. Skin injuries were localized in the regions of the head (20%) and rear legs (2%), while 24% of sows showed multiple localization; 3% of the MG sows were lame. Any lesion was recognized in CG at T1. At T2, the percentage of injured sows in MG decreased to 27%, while 1 sow from CG displayed a superficial skin lesion on the rear leg. Most MG sows showed multiple injuries (10%) and lameness (7%). Overall, 15 sows were culled for replacement, but Group had no effect on the culling rate. Among the remaining sows, 87 were inseminated with an overall 74.7% pregnancy rate (72.9% and 75.9% in MG and CG, respectively, difference p>0.05). According to the multivariable logistic regression, any fac-tor significantly affected the pregnancy rate in MG and CG sows. These results suggested that housing sows after weaning in the multiple group with a reduced number of herd mates induced a stress due to competition for establishing hierarchy, even if this condition was quickly overcome and no negative effects of group housing were observed on the weaning-to service interval and pregnancy rate.