SOCIAL RANK AND DISEASE SUSCEPTIBILITY IN PIGS

Two experiments were carried out to investigate the inter-individual v ariation in immune reactivity and disease susceptibility of group hous ed pigs of different social status. The social status of the individua l pig was determined by the outcome of social ranking fights and food competition tests. On Day 75 after the start of both experiments, all pigs were challenged with 0.5 ml of an Aujeszky disease virus (ADV) in each nostril. Data combined from both experiments showed that mortali ty and/or morbidity after the ADV challenge was highest among subordin ates. In both experiments, a lymphocyte proliferation assay, using pur ified ADV as an antigenic stimulus, showed that dominant pigs had sign ificantly higher counts per minute than subdominant and subordinate pi gs. Kendall's partial correlations showed that morbidity had been asso ciated with high values in haematological and clinicochemical blood pa rameters and not with social status of the individual pig. In each exp eriment, maternal derived antibodies against the ADV and the antibody level after the ADV challenge hardly differed between pigs of differen t social status. Major histocompatibility complex typing of class I an d II by iso-electro focusing of all pigs in Experiment 2 showed that n ot all haplotypes were distributed equally among dominant, subdominant and subordinate pigs. The present work shows that there are large ind ividual differences in immune reactivity and disease susceptibility wh ich appear to be related to the social status of the individual pig in a stable social structure.