Review: Updated scientific evidence on the welfare of gestating sows kept in different housing systems

Gestation sow housing is a contemporary animal welfare issue with legislative actions in the United States to ban individual gestation sow systems. This review sought to summarize the scientific literature since earlier reviews were published in 2004 and 2005. Seventeen papers comparing effect of housing systems on the welfare of gestating sows were published from 2005 to 2012. Stalls or crates, tether housing, and group pens including conventional group pens, loose-house pens, electronic sow feeders pens, and hoop barns were reported. The majority of recent findings were similar to the previous conclusions from papers and reviews. Cortisol concentrations were not different between stalled and group-penned sows but were higher shortly after mixing in concert with increased sow aggression and skin lesions. The effects of gestation housing system on neutrophil:lymphocyte ratio were still mixed. In the recent literature, stereotypies were greater among stalled sows compared with group-penned sows, which may reflect a change in sow genetics, because the basic housing systems have not changed. Recent papers indicated more sitting or standing inactive, leg and claw problems, and higher farrowing rate (in some studies) among stalled sows. Other studies reported more lying down among group-penned sows and no differences in other reproductive and productivity measures between stalled and group-penned sows. Weaning-to-estrus intervals were similar between stalled and group-penned sows in contrast to previous reviews that observed a shorter interval among stalled compared with grouped sows. In conclusion, recent papers found similar productivity, physiology, health, and behavior among individually or grouped sows during gestation.