The effect of preferential associations on the reproductive performance of group-housed sows

Abstract

The investigation of social bonds as a measure to improve reproduction in farmed species is an underrepresented research area. This study investigated the effects of preferential associations between group housed sows (average herd size, n = 59) on stillborn and crushed piglet numbers. Preferential associations were described as resting within < 1 m of a conspecific in which the proximity was tolerated > 60 s. The study occurred over 63 consecutive days, broken down into three 21-day periods referred to as cycles. The 21-day cycles represent the time between reintegrating events. Seven days per cycle were selected for observations providing 63 h of footage covering the functional areas of the barn. Production data were taken from one farrowing that occurred after a sow had been transferred from the barn to the farrowing house during the study period. For group-level analysis, the sows were categorised as socially prominent or non-socially prominent. Social prominence is defined as an individual that engages in significantly higher levels of interactions than their sub-group conspecifics. The subgroups were determined by our previous work that identified assortment by social connectivity within the same study herd. Each subgroup was defined as a k-core, in which the k-value represents the level of connectivity of those in the group (i.e., subgroup K1 means sows are connecting with at least one other conspecific). For individual-level analysis, sows were categorised as a sow with stillborn (at least one stillborn piglet) or a sow without stillborn (no stillborn piglets) and as a crushing sow (at least one crushed piglet) or a non-crushing sow (no crushed piglets). Degree centrality was applied to determine the number of interactions that individuals initiated and received. Results showed no overall effects of social prominence on live-born piglets (p = 0.436). Socially prominent sows demonstrated a lower mean rate of stillborn than non-socially prominent sows. Sows with stillborn had significantly lower degree centrality than sows without stillborn (p < 0.05). The numbers of crushed piglets between socially prominent and non-socially prominent sows were variable with crushing sows demonstrating significantly higher degree centrality than non-crushing sows (p < 0.05). Overall, the evidence does not provide a clear relationship between social prominence during gestation and the reproductive outputs of sows. Therefore, further work is required to validate the effects of social position in affiliative networks on the production indices of farmed pigs.