Factors Associated with Digestibility in Nursery Pigs under PRRS Infection

Abstract Text: Much work is ongoing to understand the impact of the porcine reproductive and respiratory syndrome (PRRS) on growing pigs.  A region on pig chromosome 4, with single nucleotide polymorphism (SNP) WUR10000125 (WUR), has been shown to be associated with host response to PRRS infection, based on weight gain and serum viremia. However, little is known about the association this SNP has with energy and dry matter digestibility in PRRS infected pigs.  Therefore, the objective of this study was to characterize total tract digestibility in pigs infected with PRRS and to assess the effect of the WUR SNP, weight gain (WG), and viremia on digestibility traits.  A total of 107 commercial pigs (7.6 ± 1.42 kg BW) from two trials of the PRRS Host Genetics Consortium (PHGC) were infected with PRRS isolate KS 06-72109 between 24 and 45 days of age.  Blood samples and body weights were collected weekly through 42 days post infection (dpi).  Pigs were fed ad libitum a standard corn-soy diet containing the digestibility marker titanium dioxide.  Viral load (VL) was calculated as area under the curve for q-PCR viremia through 21 dpi. Fecal grab samples were collected individually during peak viremia, 9-16 dpi, and pooled within pig, with at least 3 samples per pool. These pooled samples were used to determine apparent total tract digestibility coefficients for dry matter (DM%) and energy (En%). Traits were analyzed with a mixed model, with fixed effects of trial, parity (1-8), WUR SNP genotype (AA and AB), covariates of initial age, VL, and 0-21 dpi WG (WG21), and dam and pen(trial) as random effects.

Phenotypic correlations of WG21 with DM% (-0.03) and En% (-0.04), and of VL with DM% (-0.01) and En% (-0.11) were not significant, nor were the effects of WG21 and VL in the models for DM% and En% (P>0.05).  WUR genotype showed a significant association with En% (P=0.043), but not with DM% (P>0.05).  The AA genotype had greater En% (83.8%) than AB (82.9%). This work indicates that the genotype at the WUR SNP may be associated with feed energy digestibility.  However, the impact of reduced feed intake during a PRRS challenge on apparent total tract digestibility and post-absorptive feed utilization must be considered in future studies.  

This work was supported by PRRS Cap, USDA National Needs Graduate Fellowship Competitive Grant no. 2013-38420-20496, National Pork Board (12-151), and the PRRS host Genetics Consortium.

Keywords: WUR, gain, viremia