High indigestible dietary protein impairs growth and health status of nursery pigs with <i>Salmonella</i> Typhimurium more than with enterotoxigenic <i>Escherichia coli</i> F4 challenge

Indigestible dietary protein content is an emerging dietary concept that is thought to be related to adverse intestinal health outcomes and increased incidence of pathogen-related diarrhea in pigs. The objective of this study was to examine the effect of IDP on growth performance, immune status, and fecal consistency score (FCS) of nursery pigs challenged with enterotoxigenic Escherichia coli F4 (ETEC) or Salmonella Typhimurium (ST). Thirty-two mixed-sex nursery pigs with an average initial body weight of 7.26 ± 0.40 kg were individually housed and randomly assigned to 1 of 2 dietary treatments for 14 d in a completely randomized design (n = 8 pigs/treatment). Corn-soybean-based diets were formulated to contain similar dietary protein (DP) content (21%) but differed in IDP content [low IDP, 2.74% (LIDP) or high IDP, 4.2% (HIDP)]. After a 7-d pre-inoculation period, all the pigs were orally inoculated with either 1.36 × 106 CFU·mL-1 ETEC or 1.14 × 1010 CFU·mL-1 ST (n = 16 pigs/challenge). Growth performance, rectal temperature, FCS, and blood inflammatory biomarkers were measured pre- and post-inoculation. There was no dietary effect on any measures pre-inoculation. Inoculation with ETEC or ST increased rectal temperature, FCS, blood inflammatory cytokines, acute-phase protein, and redox biomarkers (P < 0.05). Unlike in ETEC-inoculated pigs (P > 0.05), HIDP decreased average daily feed intake and average daily gain (P < 0.05) and tended to decrease gain: feed (P < 0.10) compared to LIDP in ST-inoculated pigs. Low IDP reduced FCS (P < 0.05) and tended to reduce ileal and cecal ammonia-nitrogen concentrations (P < 0.10) in ST-pigs compared to HIDP but not in ETEC-inoculated pigs. Regardless of enteric pathogen, HIDP stimulated immune response with higher serum interleukin-6 and plasma haptoglobin compared to LIDP (P < 0.05). In ST-inoculated pigs, HIDP further increased serum albumin, tumor necrotic factor-alpha, and diamine oxidase, pathogen translocation to mesenteric lymph node, while reducing plasma reduced glutathione (GSH) and GSH: oxidized glutathione (P < 0.05). Increasing IDP content results in negative outcomes on performance, fecal score, and inflammation in ST-inoculated pigs, with milder outcomes under ETEC challenge.