Effect of Social Rank on Well-Being and Space Utilization of Dry Sows Kept in a Free Access Stall-Pen Housing Environment

The primary objective of this pilot study was to evaluate the impact of social rank on the well-being of gestating sows housed in a free access stall-pen housing environment. At d 30 post-breeding, 32 multiparous crossbred sows in groups of 4 were allocated to a stall-pen housing environment. Blood samples were taken at gestational d 30 (before mixing) and d 31 (24-h post-mixing), and then again at d 89 and 110; whereas, sow behavior was recorded at gestational d 30, 66, 87, and 102. Social rank was determined based on aggressive encounters, dyadic fighting wins and losses, and displacements between sows by 48-h post-mixing. At d 31 (post-mixing), regardless of social rank, total WBC decreased and, lymphocyte counts increased, but % change was more significant among the subordinates than dominants. The same trend occurred with neutrophil chemotaxis increased more in subordinates, but ConA-induced lymphocyte proliferation increased more in dominants, whereas LPS-induced lymphocyte proliferation was reduced among dominants. Sow behavior was differentially affected by social rank and time-periods or gestational day, with subordinates spending more time sitting and drinking, especially during time-periods 1, 3, and 4. Dominants displayed more oral-nasal-facial behaviors during mid-gestation but more sham-chew during time-period 2, which included feeding time. Social rank also influenced the percentage of time sows spent in either the stall or pen area, with subordinates in stalls and dominants in pen. These data imply that social rank differentially influences physiology and behavior of dry sows housed in a free access stall-pen environment. More specifically, the location of the dominant sow, time of day, and activity may influence when and where the subordinates spend their time within this housing system.