Group is an essential resource for gregarious animals. Dairy cows are however frequently (re-)grouped according to productivity and reproductive state leading to an unstable social environment for the animals. The present study aimed at investigating whether cows maintain social relationships in a dynamic group. Therefore we analysed whether more familiar cows spend more time in close proximity, and interact more often in an affiliative way. Social interactions and direct neighbours during feeding and resting of 12 Holstein cows (1st to 3rd lactation) in a dynamic dairy cow group of 50 animals were assessed continuously over four days using focal animal sampling. A principal component analysis over the twelve assessed social behaviour variables per pair revealed four main components: social relationships may be characterised by time spent as direct neighbours when feeding and interacting affiliative as well as agonistically (excluding displacements), by displacement success, allogrooming interactions, and time spent as direct neighbours when resting. Long-term (shared youth experience, shared adult experience) and short-term (shared dry-period, synchronised group entry) familiarity was associated with higher scores for interacting and being direct neighbours when feeding ( p< 0.05 for shared youth experience, shared adult experience, and shared dry-period), allogrooming (p < 0.1 for shared adult experience × shared dry-period), and being direct neighbours when resting (p < 0.05 for shared youth experience × shared adult experience). Long-term familiarity had a stronger effect on the intensity of social relationships, i.e. regarding investment of time and energy, than very recent shared experience. These results support the notion that dairy cows actively maintain valuable dyadic relationships. In practical terms, keeping well-acquainted cows together may contribute to a stable inner structure of a dairy herd and thus promote dairy cow welfare