Characterization of PRRS progression in growing gilts using metabolic, cytokine and complete blood count data

Abstract Text: The metabolic and immune responses of pigs inoculated with porcine reproductive and respiratory syndrome (PRRS) were assessed using canonical discriminant analysis (CDA) of multiple blood parameters. Twenty-four gilts (BW 16±4.4 kg) were selected based on high versus low growth rate over 56 days following an I.M. PRRS virus challenge in a commercial setting. Blood samples were collected on 0, 7, 14, and 28 days post-inoculation (dpi) for measurement of 52 metabolites (via ¹H-NMR), 17 complete blood count (CBC), and inflammatory traits (ELISA). Prior to the CDA, traits were analyzed in a univariate manner in order to identify traits that could potentially discriminate the different phases of PRRS progression at 7, 14, and 28 dpi. The univariate analyses statistical model included the fixed effects of growth rate group, infection status (infected [dpi 0] vs. uninfected [dpi 7, 14, and 21] pigs), dpi, and their interactions, age at dpi 0 as covariate, and pen as a random effect. Thirty-three traits were included for CDA based on having P<0.1 for the effects of dpi or its interactions. The first (CAN1) and second (CAN2) canonical variables were significant (P<0.01 and P=0.02, respectively) and showed squared canonical correlations of 0.95 and 0.86, respectively. While CAN1 discriminated dpi 7 and 14 from dpi 28, CAN2 discriminated dpi 7 from 14. The best discriminators were alkaline phosphatase (ALP) and haptoglobin for CAN1 and C-reactive protein (CRP), glucose, and insulin for CAN2. However, samples from 7 dpi had low values of CRP, glucose and insulin compared to dpi 14. Additionally, urea showed potential discriminating power, with high values on dpi 7 & 14 compared to 28 (CAN1), whereas the amino acids alanine, proline, and threonine were good discriminators of dpi 7 and 14 (CAN2). We infer that during early stages of PRRS infection (dpi 7 and 14), amino acid mobilization is increased (CAN2) for immune protein synthesis and energy requirements, whereas protein catabolism is increased in later stages (dpi 28; CAN1). Altogether, these results indicate dynamic changes in immune and energy requirements for pigs growing through a PRRS challenge. Supported by the IPPA grant#12-113.

Keywords: porcine reproductive and respiratory syndrome, residual gain, canonical discriminant analysis