During the formation of new social groups, temporal variations in behavioral associations between individuals can provide information about the role of behaviors during group formation. Although social behavior during the establishment of new groups has been studied, there is a lack of knowledge about how non-agonistic social patterns change over time.
Materials and Methods: The aim of this study was therefore to examine temporal variation in behavioral associations between individuals during the formation and maintenance of social relationships among conspecifics. The study was conducted in 15 mixed groups of commercial pigs (n = 118 pigs; 8 pigs per group), which were regrouped at the beginning of the experiment (at weaning). They were studied between 4 and 11 weeks of age to capture variation in group stability. We focused exclusively on snout-directed behavior, given its role in conspecific recognition and affiliative interactions, where snout-to-snout contact in particular may contribute to the development of social relationships. Social network analysis (SNA) was used to study temporal associations.
Results: The results show that the pigs had frequent nose-to-nose contacts (on average 33 times/15 min.) and that interactions were relatively more affiliative than aggressive (tenure range: 0,52-0,61), and more affiliative during the high social stability phase than during the medium phase (p = 0,02). As group integration progressed, the number of social partners involved in nose-to-nose contact decreased, while the frequency of nose-to-nose contact per individual increased. There was no evidence of non-random social preferences or centralized associations (centralization degree range: from 0 to 0,3). The pigs showed more nose-to-nose contacts with animals from different litters than with those from the same litter (i.e., heterophilous association based on litter origin; assortativity range: from -0,34 to -0,08) and between individuals with different early social experiences (assortativity range: from -0,45 to -0,07) across all integration phases.
Furthermore, males initiated contacts more frequently than females, while females occupied more central positions within the social network.
Conclusions: These behavioral processes, which support the formation and maintenance of social relationships, demonstrate that non-agonistic behaviors such as snout contact play a prominent role in the social dynamics of pigs.
Sunil Khatiwada, Victoria Lee, Simon P. Turner, Irene Camerlink, Temporal social network structures based on snout contact during group integration in pigs, Applied Animal Behaviour Science, 2025, 106838, ISSN 0168-1591, https://doi.org/10.1016/j.applanim.2025.106838.