As dairy cows’ needs and demands change over the different phases of their reproductive cycle, regrouping is common practice in dairy farming to facilitate management and handling. However, social instability associated with regrouping is known to have negative effects on the cows, including disturbances in their lying behaviour. In this study, we examined the effect of familiar group mates on lying time and lying synchrony in a dynamic group of approximately 50 early lactating dairy cows during 23 regrouping events. We focussed on 13 primiparous and 33 multiparous post partum cows during 24 hours after their introduction to the group as compared to a matched control sample of resident cows. We hypothesised that freshly introduced cows would lie shorter and behave less synchronously with the group as compared to resident cows. Further, we hypothesised that lying duration and lying synchrony will increase with the number of familiar animals present and that these effects may depend on whether the familiarity was acquired early in life or only recently.
As predicted, primiparous fresh cows lied less and behaved less synchronous at the dyadic level than their matched residents. However, no such effect was present in multiparous cows. The presence of recently familiar animals had no influence on either primiparous or multiparous cows’ behaviour. In contrast, early familiar animals affected the cows’ behaviour in several aspects, yet differently in primiparas and multiparas. In fresh primiparas, an increasing number of early familiar animals present had a negative effect on lying duration. Among both fresh and resident primiparas, early familiar dyads were more synchronized than other pairs of animals. In multiparous cows, a higher number of early familiar cows present led to more synchronous behaviour with the group.