Evaluation of a QTL for Porcine Circovirus Type 2b (PCV2) Viral Load on Long-Term Growth Performance and Nutrient Digestibility in Inoculated or Vaccinated Pigs for PCV2

A previous experiment evaluated pigs selected for a PCV2-susceptibility marker QTL (C, resistant; T, susceptible) and were inoculated (PCV) with or vaccinated (VAC) against PCV2 in the nursery phase. Pigs genotyped for the C allele had reduced viremia and IgG production compared with the T allele when infected with PCV. Two experiments were conducted to evaluate growth performance through the finishing phase. A model was used to assess the residual between final and predicted BW on pigs from the previous trial. Pigs with a low or high net residual were used for Exp. 1 or Exp. 2 respectively. In Exp. 1, a total of 40 pigs (38.5 kg; 8 pigs/treatment) were selected from (genotype-PCV status): CC-PCV, CT-PCV, TT-PCV, CT-VAC, and TT-VAC. Pigs were housed by treatment, 2 pigs per pen, 4 pens per treatment. In Exp. 2, 4 pigs from each residual, high (41.9 kg BW) and low (30.2 kg BW), were selected from the following (genotype-PCV status): CT-PCV, TT-PCV, CT-VAC, and TT-VAC, for a total of 32 pigs, housed individually. All pigs had ad libitum access to a 4-phase grow-finish corn-soybean meal diet that met or exceeded the NRC (2012) requirements, with titanium dioxide as an indigestible marker. Growth performance was measured every 14 d; whereas, blood and fecal samples were collected at the end of each phase. Loin eye area and backfat were determined via ultrasound at the end of phase 4 and HCW was determined at harvest. For Exp. 2, data was analyzed using initial BW as a covariate. In Exp. 1, ADFI in phase 1 was reduced in the CC-PCV group compared with TT-PCV (P < 0.05). In phase 3, ADFI was reduced in VAC group compared with the PCV group (P < 0.05). In phase 1 thru 3, digestibility of GE and DM were greater in the CC-PCV group compared with TT-PCV (P < 0.05). In Exp 2., low residual pigs had greater G:F during the phases 2 and 3 (P < 0.05). No differences were found for GE and DM digestibility between groups (P > 0.10). Pigs with the CT genotype were found to have less backfat (P < 0.10), and greater lean (P < 0.05) and percent lean (P < 0.05) than those with TT genotype with no difference in BW. Together these data suggest that the PCV2-susceptibility marker genotype may affect ADFI, nutrient digestibility, and carcass traits during the growing-finishing period.