Genes with major effects on clinical, pathological and microbiological outcome of porcine pleuropneumonia

Actinobacillus pleuropneumoniae (A. pleuropneumoniae) is among the most important pathogens in pork production. The pathogen can cause severe economic losses due to acute or chronic pleuropneumonia accompanied by decreased performance and increased mortality. Both, therapeutic treatment and vaccination have no sustainable effect on the control or spreading of infection and in addition, vaccines are not always available. Thus, our research targets the identification of genetic markers for the resistance/susceptibility to pleuropneumonia. Such markers may be used in classical or genomic selection for A. pleuropneumoniae control, sustainable improvement of porcine health, production efficacy, animal welfare and consumer protection.

For achieving this aim, populations with high or low susceptible pigs based upon genetics, shortest possible linkage groups and an accurate and repeatable technology for a precise challenging and phenotyping of pigs are the major requirements. Therefore A. pleuropneumoniae serotype 7 was used in a standardized aerosol infection model and genetics were analysed by microarray-based differential expression studies and QTL analysis.

Seven days post infection significant differences were found within different pig populations but also between litters (clinical scores 0.3 vs. 4.3). Resistance/susceptibility segregated within Large White, Landrace and Pietrain breeding lines, with highest resistance in Hampshire and highest susceptibility in Pietrain and Landrace pigs. Genes and pathways central for the defence and pathogenesis of pleuropneumonia were identified in expression analysis and gene effects, each of them explaining up to 20% of phenotypic variance, were mapped to chromosomes 2 and 12. A hotspot for gene regulation of A. pleuropneumoniae defence was mapped to chromosome 13. Two of the identified markers in combination explained 100% of deaths and 90% of enhanced clinical scores.

Populations with short linkage groups (commercial breeds), segregating for genetic resistance/susceptibility to A. pleuropneumoniae do exist. Identified singular genes explaining up to 20% of variance could therefore be used in genetic health selection programs. However, so far markers are not mapped as precisely as necessary for implementation in practical selection and functional genes and variants still await identification. A next generation sequencing experiment on selected pigs differing extremely in A. pleuropneumoniae susceptibility has been started to detect these pending basic functional gene variants.

Disclosure of Interest: None Declared.