2013 Annual Report
1a.Objectives (from AD-416):
Continued losses to the pig industry from porcine reproductive and respiratory syndrome (PRRS) make it imperative to search for alternative PRRS control practices. This grant proposes to use state-of-the-art whole genome association analyses to identify the genetic determinants of resistance/susceptibility of commercial U.S. swine to PRRSV infection. We will address PRRS coordinated agricultural project (CAP2) Objective 3: Characterize host factors that contribute to PRRS disease resistance and susceptibility (host genetics). The primary samples to be tested will be those collected through the National Pork Board-funded PRRS Host Genomic Consortium (PHGC), a national effort to collect phenotypic data to assess the role of genetics in determining pig resistance to PRRSV infection and related pathology and growth effects. DNA samples from PHGC pigs will be genotyped with the newly developed 60K single nucleotide polymorphism (SNP) chips. Obj.3.1. addresses research on immunity and vaccination using gene expression analyses to reveal new PRRS response pathways that can be targeted for vaccines, drugs, and biotherapeutics to prevent and treat PRRSV infections. Obj.3.2. will use whole genome association studies to reveal new genetic alleles associated with PRRS resistance/susceptibility. The extensive genomic (SNP) analyses will find allele variants that determine resistance/susceptibility of commercial U.S. swine to PRRSV infection.
1b.Approach (from AD-416):
Extensive whole-genome association analyses will be performed to determine which markers are associated with PRRS susceptibility/resistance traits. Simultaneously gene expression analyses are planned to determine PRRS response pathways and critical candidate genes that differ in expression between PRRS-resistant versus susceptible PHGC pigs and to dissect pathologic versus protective immune responses in samples collected from PRRSV-infected versus vaccinated swine. Overall the proposed studies will identify genetic determinants of resistance/susceptibility of commercial U.S. swine to PRRSV infection. This information will be disseminated to swine breeders, genetics companies, and genotyping services so that sets of these recommended genetic markers can be employed in future breeding programs to increase disease resistance.
State-of-the-art genome wide association studies (GWAS) were performed and identified a region on swine chromosome 4 (SSC4) that is associated with resistance/susceptibility of commercial U.S. swine to Porcine Reproductive and Respiratory Syndrome (PRRS), the most economically important pig disease worldwide. ARS researchers at Beltsville, Maryland, worked with scientists from Iowa State, Washington State, Purdue, and Michigan State universities to analyze samples and data collected through the U.S. PRRS Host Genomic Consortium (PHGC), a national effort to collect phenotypic data to assess the role of genetics in determining pig resistance to PRRSV infection and related pathology and growth effects. Analyses of the first 5 PHGC trials of commercial pigs from 3 different genetic sources affirmed that serum viremia and weight gain after infection were moderately heritable at 0.39 and 0.34, respectively. At Iowa State University extensive GWAS were performed on data from PHGC1-5 data resulting in the identification of regions on swine chromosome 4 (SSC4) and SSCX that are involved with viral load and SSC1, 4, 7, 17 for weight gain. In fact, the SSC4 region accounts for 15% of the variation in viral load and 11% for weight gain after infection. Genomic estimated breeding values (GEBV) for the SSC4 region were perfectly and favorably correlated at -1, i.e., for the desired effect of decreased virus and increased weight. Thus, our results affirm that pig response to experimental PRRSV challenge has a strong genetic component with a major locus on SSC4 explaining a substantial proportion of the genetic variance. In addition, this resistance allele is found in major pig breeds, Landrace, Large White, Yorkshire and Duroc. These results are already being utilized by the swine industry and are enabling geneticists to develop plans for marker-assisted selection of pigs with improved response to PRRSV infection. This information has been disseminated to swine breeders, genetics companies, and genotyping services so that sets of these recommended genetic markers can be employed in future breeding programs to enhance PRRS disease resistance.
Boddicker, N., Wade, E.H., Rowland, R., Lunney, J.K., Garrick, D.J., Reecy, J., Dekkers, J.M. 2011. A major QTL associated with host response to Porcine Reproductive and Respiratory Syndrome virus challenge. Journal of Animal Science. 90:1733–1746.