The effect of age, environment and management on social contact patterns in sheep

Abstract

Social structures of group-living farm animals can have important implications for animal welfare and productivity. Understanding which factors can have an effect on social behaviour is thus important in order to develop the best management strategies in livestock industries. Here, we studied the social network structure of a flock of 84 Poll Dorset ewes and collecting dyadic associations data through the use of proximity sensors during two study periods. First, we analysed the social structure of ewes at a group-level, by analysing the community structure, and at individual-level, by determining whether the ewes showed social differentiation in their association patterns. Second, we measured for the contribution of genetic relatedness, age, weight, reproductive status and previous management sub grouping on social associations to test for homophily effects. Lastly, we evaluated whether social clustering was influenced by the stocking density of individuals in a field, and by weather parameters, through the use of two climatic indices, the Temperature-Humidity Index (THI) and the Wind Chill Index (WCI). Our results showed that the pairwise associations between ewes are not-random and highly heterogeneous, both in total time spent in contact and in contacts duration. There was no evidence that ewes were subdivided into social communities, and at individual level, they showed markedly differentiated social relationships, demonstrating preferences in social ties. However, the factors that influenced the preferred social interactions between individuals changed over time. In the first study period ewes tended to maintain the social bonds formed in previous management sub grouping, most likely due to a social familiarization resulting from repeated interactions with the same individuals. In the second study period similarity in age influenced the strength of associations among ewes. We found no significant influence of reproductive status, weight (as an indicator of body size) and genetic relatedness on proximity associations in either study period. Moreover, our results showed the tendency of the ewes to form social clusters varied in relation to animals’ density, and Wind Chill Index (WCI). The identification of conditions that modify the social behaviour of sheep is critically important in order to implement management and productivity strategies and our results highlight how flock social structure can change depending on environmental and social contexts.