Many animals live in highly structured groups. Individual differences in the number and identity of social contacts define the social network structure. Most domesticated animals belong to such species. The composition of groups can be disturbed by grouping animals according to age or production stage, which can in turn induce stress. We investigated whether the preference of two animals to stay together depends on their sociality or on the composition of the group. We observed 158 dairy cows in six pens during 17 weeks. The precise positions of the cows were monitored with positional loggers 24/7 in stable groups and during the formation of new groups. In stable groups, the sociality of a cow was maintained over the entire observation period. When introducing foreign individuals into well-established social groups, the sociality of individual cows was maintained independently of the group; this sociality was therefore not necessarily defined by the time spent in the group. During the formation of new groups, newly introduced cows dynamically interacted with resident ones, forming a few strong short-lasting contacts between newcomers and resident cows. However, most long-lasting interactions occurred between resident group members. Our study reveals that in a species that spontaneously lives in large social groups, such as cattle, each animal has its own sociality independent of group. However, when it comes to establishing strong relationships between newcomers and resident animals, more than two weeks is needed.