Impact of viral disease hypophagia on pig jejunal function and integrity

Abstract

Pathogen challenges are often accompanied by reductions in feed intake, making it difficult to differentiate impacts of reduced feed intake from impacts of pathogen on various response parameters. Therefore, the objective of this study was to determine the impact of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) and feed intake on parameters of jejunal function and integrity in growing pigs. Twenty-four pigs (11.34 ± 1.54 kg BW) were randomly selected and allotted to 1 of 3 treatments (n = 8 pigs/treatment): 1) PRRSV naïve, ad libitum fed (Ad), 2) PRRSV-inoculated, ad libitum fed (PRRS+), and 3) PRRSV naïve, pair-fed to the PRRS+ pigs' daily feed intake (PF). At 17 days post inoculation, all pigs were euthanized and the jejunum was collected for analysis. At days post inoculation 17, PRRS+ and PF pigs had decreased (P < 0.05) transepithelial resistance compared with Ad pigs; whereas fluorescein isothiocyanate-dextran 4 kDa permeability was not different among treatments. Active glucose transport was increased (P < 0.05) in PRRS+ and PF pigs compared with Ad pigs. Brush border carbohydrase activity was reduced in PRRS+ pigs compared with PF pigs for lactase (55%; P = 0.015), sucrase (37%; P = 0.002), and maltase (30%; P = 0.015). For all three carbohydrases, Ad pigs had activities intermediate that of PRRS+ and PF pigs. The mRNA abundance of the tight junction proteins claudin 2, claudin 3, claudin 4, occludin, and zonula occludens-1 were reduced in PRRS+ pigs compared with Ad pigs; however, neither the total protein abundance nor the cellular compartmentalization of these tight junction proteins differed among treatments. Taken together, this study demonstrates that the changes that occur to intestinal epithelium structure, function, and integrity during a systemic PRRSV challenge can be partially explained by reductions in feed intake. Further, long term adaptation to PRRSV challenge and caloric restriction does reduce intestinal transepithelial resistance but does not appear to reduce the integrity of tight junction protein complexes.

Fig 1

A-C. Representative RNAscope duplex for Occludin (brown) and ZO-1 (red). A) Pigs were either PRRSV naïve and fed ad libitum (Ad); B) PRRSV naïve and pair-fed to PRRS+ pigs intake (PF); or C) challenged with PRRSV (PRRS+).

Fig 2

Representative immunohistochemistry images for Claudin 2 (A-C), Claudin 4 (D-F), and ZO-1 (G-I). Pigs were either PRRSV naïve and fed ad libitum (Ad: A, D, and G), PRRSV naïve and pair-fed to PRRS+ pigs intake (PF: B, E, and H), or challenged with PRRSV (PRRS+: C, F, and I). Pigs were euthanized at days post inoculation (dpi) 17. Staining was limited to the epithelial cells, with higher stain density at cell membranes.