The usefulness of heart rate variability (HRV) and heart rate (HR) for documenting short and long term effects of two different changes in the social environment - (I) grouping and (II) grooming simulations - of pigs was examined. Grouping is known as a stressful event for pigs, because a new group hierarchy has to be established. Pigs are grooming each other and the behaviour of the recipient indicates a state of relaxation. A quantitative Lorenz plot analysis was used to calculate two HRV-parameters: the SD1, which correlates to the vagal tone and the SD2, depending on overall activity of all components which control heartbeat. In order to minimise the influence of motor activity on SD1, SD2 and HR, only those valid 5-minute-periods of non-invasive telemetric measurements of succeeding beat-to-beat intervals were taken into account, in which pigs remained in recumbency. (I) In a housing experiment, 16 single housed pigs were grouped into 4 groups of 4 pigs at the age of 22 weeks. In pens of 2 groups, objects for manipulation were available. Eight other pigs remained in single housing. From week 20 to 25, individual medians of HR, SD1 and SD2 from all valid 5-minute-periods per week were calculated. After grouping, HR increased and SD1 decreased compared to week 21 (p (II) In a second experiment, grooming was simulated by massaging eight single housed pigs along their head and belly with fingers by the experimental handler during 5-minute-periods of grooming-simulation (3 simulations per pig/day on 4 days per wk during wk 26 and 27). Experimental grooming increased HR while SD1 decreased (p It can be concluded that HR and HRV measurements provide valid information about the long term effects of changes in the social environment on pigs. The application of HRV, especially those HRV-parameters which reflect the vagal tone like SD1, can be a sensitive tool to address problems in applied animal research.