Validation of the Effects of a SNP on SSC4 Associated with Viral Load and Weight Gain in Piglets Experimentally Infected with PRRS virus

Abstract Text:

Porcine reproductive and respiratory syndrome (PRRS) is the most costly disease to the US pork industry, and vaccines, biosecurity measures, and proposed methods for eradication have had limited success. The aim of the PRRS Host Genetics Consortium (PHGC) is to identify genomic markers and pathways associated with host response to PRRS virus (PRRSV), which could potentially be used for genetic selection of pigs for increased resistance or reduced susceptibility to the virus. Boddicker et al. (2012) identified a SNP on SSC4 (WUR10000125) for which the favorable allele (B) was associated with reduced viral load (VL) and increased weight gain (WG) under infection with the NVSL-97-7895 PRRSV isolate. The objective of this study was to test the effects of this SNP when infecting pigs with a genetically different isolate of PRRSV (KS-2006-72109), which has 89% amino acid sequence identity with NVSL-97-7895 in GP5. Following the same experimental design, ~200 commercial crossbred piglets per trial for a total of 5 trials were experimentally infected with PRRSV at 28-35 days of age. Blood samples and weights were collected periodically for up to 42 days post infection (dpi). Viremia was measured using a qPCR assay for PRRSV RNA, and VL was defined as the area under the curve of Log viremia from 0-21 dpi. WG was defined as weight gain from 0 to 42 dpi. Analyses were carried out using PROC MIXED in SAS (v9.2), with trial nested with parity and the number of B alleles for the SSC4 SNP as fixed effects, weight and age at infection as covariates, and litter and pen nested within trial as random effects. Consistent with previous findings, individuals that were heterozygous for the SSC4 SNP had greater WG (0.95±0.32 kg, p=0.0031, n_AA=682, n_AB=167) and lower VL (-3.89±0.78 units, p<0.0001, n_AA=431, n_AB=86) compared to their AA counterparts. The size of the effect for the SSC4 SNP was approximately half the reported value for the NVSL-97-7895 isolate for WG (0.95±0.32 vs 2.0±0.4 kg), but comparable for VL (-3.89±0.78 vs -4.1±0.6 units). These results suggest this SSC4 marker may be useful for genetic selection of pigs for increased resistance or reduced susceptibility to PRRSV isolates that differ genetically and possibly in pathogenicity. This work was supported by Genome Canada, USDA ARS, and breeding companies of the PHGC and PigGen Canada.

Keywords: PRRS, SSC4, Genetic Selection