Increased group size reduces conflicts and strengthens the preference for familiar group mates after regrouping of weaned dairy calves (Bos taurus)

The objective of the present study was to investigate how group size and familiarity influence daily activity and social interactions in regrouped dairy calves. A total of 84 calves were divided into groups of 4, 8 and 16 animals, in which half of the calves in each group were unfamiliar with each other. Daily activity, incidences of social interactions and play behaviour were recorded on days 1, 3 and 11 after regrouping. Time spent feeding and resting were not significantly affected by group size, but calves in larger groups spent more time feeding (P < 0.05) and lying (P < 0.01) close to one another than calves in groups of four. Calves in groups of 16 were more active (P < 0.05) and spent less time standing inactive (P < 0.05) than calves in smaller groups. The number of displacements from the feed barrier was higher in groups of four than in larger groups (P < 0.05), and more displacements were directed towards unfamiliar calves (P < 0.01). However, the level of agonistic behaviours and the number of displacements from the resting area, occurrence of mounting, cross-sucking, social grooming and play behaviour was not affected by group size. Calves in groups of 16 were found laying close to familiar calves more frequently than to unfamiliar calves (P < 0.01) and they directed more social grooming towards familiar calves (P < 0.01). In conclusion, calves in larger groups are generally more active, displace other calves less frequently from the feed barrier, show increased proximity to other calves and perform more positive social interactions with familiar calves the first 1–3 days after regrouping.