Social rank and disease susceptibility in pigs.

Two experiments were carried out to investigate the inter-individual variation in immune reactivity and disease susceptibility of group housed pigs of different social status. The social status of the individual 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 mortality and/or morbidity after the ADV challenge was highest among subordinates. In both experiments, a lymphocyte proliferation assay, using purified ADV as an antigenic stimulus, showed that dominant pigs had significantly higher counts per minute than subdominant and subordinate pigs. Kendall's partial correlations showed that morbidity had been associated with high values in haematological and clinicochemical blood parameters and not with social status of the individual pig. In each experiment, maternal derived antibodies against the ADV and the antibody level after the ADV challenge hardly differed between pigs of different social status. Major histocompatibility complex typing of class I and II by iso-electro focusing of all pigs in Experiment 2 showed that not all haplotypes were distributed equally among dominant, subdominant and subordinate pigs. The present work shows that there are large individual differences in immune reactivity and disease susceptibility which appear to be related to the social status of the individual pig in a stable social structure.

Effect of climatic stress on the immunological reactivity of weaned pigs.

Weaned pigs exposed daily to either unpredictable draught (experiment 1) or intermittent unpredictable draught (experiment 2) showed different lymphocyte blastogenic responses after mitogenic stimulation with phytohaemagglutinin (PHA) and concanavalin A (ConA). In both experiments PHA skin test responses were lower for draught exposed pigs than for control pigs and leucocyte numbers or profiles were altered compared to those of control pigs. Superoxide production and chemiluminescence of porcine granulocytes were similar for draught exposed and control animals. Furthermore, serum globulin content did not differ significantly between pigs in the experimental and control room. The strong increase in serum gamma-globulin after the Aujeszky Disease Virus (ADV)-challenge was the same for draught exposed and control pigs. The same held for the lymphocyte blastogenic response with ADV protein as antigenic stimulus. The present study shows the effects of climatic stress on immunological reactivity, which may reflect a homeostatic disturbance of the pig's immune system elicited by exposure to unpredictable draught.

[Mucosal lesions in the pars esophagus in swine: prevalence and the effect of stress]. / Slijmvliesveranderingen in de pars oesophagea bij varkens: prevalentie en de invloed van stress.

Morphological investigations of slaughterhouse material revealed a prevalence of 63% of the sows (n = 224) and 36% of the slaughter pigs (n = 209) with mucosal lesions in the pars oesophagea. The mucosal lesions were composed of severe hyperkeratosis, erosions or ulceration. Microscopic examination showed that hyperkeratosis is attended with parakeratosis. From experiments in a climate controlled pighouse it could be concluded that mixing of unfamiliar pigs resulted in higher prevalences of gastric lesions as compared with keeping the litter together until the end of the experiment (farrow to finish system). There was no relation between gastric lesions and climatic stressors or between gastric lesions and growth and sex of the pigs. When pigs, according to social ranking, were divided in high, middle and low rank it showed that more pigs in the middle-ranked group had gastric lesions. The serum pepsinogen was not related with gastric lesions. There was a tendency that plasma cortisol increased with severity of gastric lesions. There was a strong significant 'litter-effect', which can indicate a genetic predisposition for the development of gastric lesions. Maybe that the presence of mucosal lesions in the pars oesophagea can be used as an objective indicator for welfare in intensive pig husbandry.

[Current possibilities of improving health and welfare status of pigs through introduction of the specific 'Stress Free' (SSF) System]. / Nieuwe mogelijkheden tot het verhogen van de gezondheids- en welzijnsstatus van varkens door introductie van het 'Specific Stress Free' (SSF)-systeem.

Health and welfare problems of pigs in intensive husbandry systems are mainly caused by housing and management of the animals. The actual structure of these systems also gives rise to health and welfare problems. Solving these problems is very difficult to achieve in the existing systems. It will be necessary to create new structures and housing systems from a preventive veterinary point of view to avoid harm to health and welfare caused by specific stressors. Specific stressors which can be prevented are associated with the risk of infection, mixing and replacing animals, high density, inadequate house climate, handling of animals and the farmer's attitude towards his animals. The SSF-system specifies the method by which these specific stressors are prevented.