Interaction between sows’ aggressiveness post mixing and skin lesions recorded several weeks later

Abstract

Group housing of pigs leads inevitably to more or less serious agonistic interactions during the establishment of the social rank order of the group. In order to reduce the number of severe agonistic interactions and thus the negative effects on well-being and performance, the use of genetic selection of calm sows maybe a possible strategy. Therefore, in this study the behaviour of 112 German Landrace sows was observed after the animals were brought together in a group of 10–20 sows. After this initial period, the sows were integrated into a large dynamic group in the dry sow area where the animals were housed for 71 days. Before moving the sows into the farrowing area, skin lesions scores for three body regions (front/middle/rear) on both sides were recorded using a scoring system from 1 (no lesions) to 4 (wounds, lesions all over the body area). After farrowing, sows’ reaction towards the separation from their litter was recorded to analyse relationships between aggressiveness and handling. Earlier research suggests that skin lesions recorded shortly after mixing are associated with agonistic interactions at mixing and might therefore be a useful indicator for the evaluation of recent aggressiveness of animals. However, results of the present study show that an individuals’ frequency of being initiator of agonistic interactions post mixing do not affect (p>0.1) the extent of skin lesion recorded 10 weeks later. Conversely, animals being attacked frequently were evaluated with higher scores in the anterior region (p=0.0435). These findings indicate that a higher skin lesion score does not represent generally more aggressive sows under commercial housing systems, but it is still an indicator for overall aggressiveness within pens or groups. Between the different groups significant differences in the extent of skin lesions were found (e.g. skin lesion score front: p=0.0228). A negative relationship was found between skin lesion score in caudal region and sows’ reaction towards stockperson when handling their piglets (r=−0.28, p<0.01). Furthermore, behaviour traits related to aggressiveness correlated with later reproductive performance. While sows recorded frequently as aggressors post mixing gave birth to more total and live born piglets, sows with higher skin lesion scores had a lower reproductive performance (e.g. skin lesion score front vs. total born piglets: r=−0.28, p<0.01). Taken together, these results suggest that more severe skin lesions are indicative of low-ranking and less vital sows, but skin lesions are not useful to identify the generally more aggressive individuals.