Swine Leukocyte Antigen Diversity in Commercial Breeding Boars: Molecular Characterization and Potential Implications on Animal Health (170.1)

The highly polymorphic swine MHC antigens (SLA) are among the most important determinants of swine immune responses to disease and vaccines, yet their diversity in commercial swine breeding stock has not been studied at the molecular level. Using PCR-based typing assays, diversity of the class I (SLA-1, -2, -3) and class II (DRB1, DQB1, DQA) genes was surveyed in ten pure-line, pedigreed boar populations (n = 413) of a major commercial pig breeder. Of a maximum possible of 623 SLA haplotypes of these loci, 44 class I and 30 class II haplotypes were identified. The three most common class I and class II haplotypes constituted a combined frequency of 33% and 36%, respectively. Half of the studied animals (48% and 53%, respectively) had at least a copy of either of these class I or class II haplotypes. Prevalence of SLA homozygosity varied significantly among boar lines, ranging between 5-70%; overall one in five animals was homozygous for all six SLA loci surveyed. Limited MHC diversity, which has been associated with poor disease outcomes in other species, may result from unintentional selection of the SLA region which links closely to many favorable production traits. Molecular breeding techniques, including the assessment of SLA, may allow breeders to unlink SLA from production traits and reduce its negative pressure. Monitoring SLA diversity in breeding and commercial herds (produced by 2, 3, or 4-way crosses of breeding stock) will ensure robust immune response.