Herd-level risk factors for chronic pleuritis in finishing pigs: a case-control study

Background Chronic pleuritis is a common finding in slaughtered pigs in post-mortem meat inspection. The prevalence of pleuritis has been increasing during the last decade also in Finland. The aim of this prospective case-control study was to search for environmental, infectious and management-related herd-level risk factors for pleuritis in the slaughterhouse. Altogether 46 Finnish pig herds, including 25 control (low pleuritis prevalence in meat inspection) and 21 case (high pleuritis) herds, were enrolled in the study and visited during the tenth week of the rearing period of finishing pigs. Herd personnel were asked about basic herd information, management and environmental factors. Selected pigs were examined clinically, environmental parameters were measured and 15 blood samples per herd were taken during herd visits. Antibodies against Actinobacillus pleuropneumonia serotype 2 (APP2) and ApxIV toxin and swine influenza virus were measured. After the slaughter of study pigs, meat inspection results of the batch were gathered from slaughterhouses. Multivariate logistic regression models were built to identify possible risk factors for a herd to be a case herd ( i.e. having high pleuritis values).Results Finishing herd type, herd size and APP2 seropositivity were observed to act as risk factors. In addition to these, general herd-level factors, flank biting and high APP2 antibody prevalence of the herd tended to be associated with the risk of the herd being a case herd. None of the other clinical signs of pigs, management-related factors or environmental measurements were associated with herd status.Conclusions As previously known, in endemic and subclinical infections such as APP, herd and management-related factors are important in building up infection pressure, but single risk factors seem to be difficult to identify. However, as flank biting was more common in high pleuritis herds, part of disease susceptibility is likely mediated via stress.