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A comparison of viremia profiles between piglets infected with one of two isolates of porcine reproductive and respiratory syndrome virus
Log serum viremia under Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection has been shown to be appropriately modelled by the Wood’s curve, which is often used to model lactation yield in dairy cattle. Previously, infection with PRRSV isolate KS-2006-72109 (KS06) was found to result in 5.8±0.7 units lower viral load (VL), defined as area under the curve of log viremia for 0-21 dpi, than infection with PRRSV isolate NVSL-97-7895 (NVSL). The objectives of this study were to: 1) compare three parameters that describe viremia profiles based on the Wood’s curve between these two isolates of PRRSV, and 2) estimate the heritabilities of these parameters for each isolate. The parameters were: time to peak viremia (TP), peak viremia (PV) and rate of post-peak clearance (CL). This study used data on three commercial crosses paired across five PRRSV infection trials with NVSL and three trials with KS06, in which ~200 piglets per trial were experimentally infected with virus at 28-35 days of age. Viremia was determined from serum collected periodically from 0-42 days post infection (dpi). A Wood’s curve and a biphasic extended Wood’s curve were compared to identify piglets with a rebound in viremia. To evaluate differences in TP, PV, and CL between isolates, phenotypes for these parameters were analyzed in a model in SAS (v9.4) that included isolate, parity and rebound (yes/no) as fixed effects, age and weight at infection as covariates, and trial, pen within trial, sire and litter as random effects. Compared to KS06, NVSL infected piglets reached peak viremia 1.87±0.60 (p=0.0161) days sooner, had 1.03±0.15 (p=0.0002) log higher PV, and cleared viremia 8.91±2.88% (p=0.0170) more quickly. To estimate heritabilities of these parameters, a similar model was run in ASReml 3.0 for each isolate, replacing sire with the genetic effect of animal using a within-breed genomic relationship matrix generated from the PorcineSNP60 Beadchip, and excluding virus and trial within virus. Heritability of TP was similar for NVSL (0.36±0.08) and KS06 infections (0.27±0.11). Heritability of PV for KS06 infections (0.43±0.09) was triple that for NVSL (0.13±0.07), and heritability of CL was higher for NVSL (0.36±0.08) infections than KS06 (0.22±0.10). This study shows that TP, PV and CL are moderately heritable and differences in these parameters are responsible for the difference in VL between NVSL and KS06. This work was supported by Genome Canada, USDA ARS, and breeding companies of the PHGC and PigGen Canada.
Keywords:
pigs, PRRSV, viremia profile