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Evaluation of a QTL for porcine circovirus type 2b (PCV2) viral load on growth performance in inoculated and vaccinated pigs for PCV2
Data from a previous PCV2b experimental challenge revealed the presence of a QTL associated with viral load, a measure of susceptibility. A study was conducted to evaluate the effects of this QTL on growth in PCV2b-experimentally infected and vaccinated pigs. Prior to challenge the pigs were genotyped for the QTL (CC, resistant; TT, susceptible; and CT) and profiled for PCV2-specific maternal antibodies. Experimental pigs were either vaccinated (VAC) at 3 wk of age, or inoculated (NOV) with PCV2b at 5 wk of age. Pigs (n = 111) were allocated to five groups; VAC included pigs with CT and TT genotypes while NOV included pigs with all genotypes. Pigs were allocated to pens by genotype-PCV2b treatment, and were ad libitum fed an antibiotic free, corn-soybean meal based nursery diet that met or exceeded NRC (2012) requirements. Titanium dioxide was added to the diet as an indigestible marker. Feed disappearance and individual BW were obtained weekly for determination of ADG and feed disappearance. Blood (for viremia analysis) and fecal samples (for microbiome analysis; data not shown) were collected weekly. Pen fecal samples were collected at wk 2, 4, and 6 for digestibility analyses (data not available). Overall, ADG, feed disappearance, and BW were not different between treatment, genotype, or treatment x genotype (P > 0.10). In the NOV group, the CC genotype had numerically greater BW than CT and TT genotypes throughout the 6 wk trial (33.9, 30.9, and 29.5 kg at wk 6, respectively). This trend, with the C allele being considered favorable, was consistent in the VAC pigs (CT = 32.8 kg; TT = 30.4 kg). Although d 7-28 viremia data showed an increased viral titer in NOV pigs as expected, the CC genotype had a reduced titer compared with the CT and TT genotypes (P < 0.05). These preliminary data suggest that selection for the CC genotype may reduce the need for PCV2 vaccination by providing greater resistance to PCV2 challenge compared to the other genotypes. However, additional research is needed to delineate the long term and cellular effects of this QTL.
Keywords:
pig, porcine circovirus type 2b, vaccine