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A proprietary antimicrobial feed additive comprised of essential oils, medium-chain fatty acids, and a toxin-adsorbing mineral showed promising bacteriostatic and bactericidal effects in vitro. This study investigated the impacts of supplementing this blend on growth, gut microbiome, and enteric disease resilience in weaned pigs experimentally challenged with an enterotoxigenic Escherichia coli (ETEC). Thirty-six weanling pigs (6.88 ± 0.30 kg body weight) blocked by weight and gender were assigned to one of three dietary treatments: control or dietary supplementation with 0.25% or 0.50% of the antimicrobial blend. This study lasted 28 d with 7 d before and 21 d after the first ETEC inoculation (day 0). All pigs were orally inoculated with 1010 CFU F18 + ETEC/3-mL dose for 3 consecutive days. Growth performance data and diarrhea scores were recorded throughout the experiment. Fecal samples collected on days -7, 0, 7, and 21 post first inoculation (PI), and ileal digesta and mucosal tissue collected on day 21 PI were further analyzed for gut microbiome using 16S rRNA sequencing. All data, except for frequency of diarrhea and gut microbiome, were analyzed by ANOVA using the PROC MIXED of SAS. The chi-square test was used for analyzing frequency of diarrhea. Gut microbiome data were analyzed using QIIME2 and visualized using the R program. Dietary supplementation of 0.25% or 0.5% of the antimicrobial blend increased (P < 0.05) feed efficiency on days 14 to 21 PI of ETEC and reduced (P < 0.05) frequency of diarrhea during the study. Compared with the control group, adding 0.5% dietary antimicrobial blend increased (P < 0.05) relative abundance of Firmicutes but reduced (P < 0.05) Bacteroidetes and Proteobacteria in feces on day 7 PI. Pigs that received the antimicrobial blend also had higher (P < 0.05) relative abundance of Lactobacillaceae, but lower (P < 0.05) relative abundance of Enterobacteriaceae in feces on day 7 PI than pigs in control. In conclusion, supplementation of this antimicrobial blend at 0.5% reduced incidence of severe diarrhea in weaned pigs challenged with F18 ETEC and enhanced feed efficiency of weaned pigs at the last week of the experiment. Supplementation of this antimicrobial blend also modified the microbiota diversity in feces and ileal mucosa of weaned pigs., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The experiment was conducted to investigate the effects of trace amounts of antibiotic on growth performance, diarrhea, systemic immunity, and intestinal health of weaned pigs experimentally infected with an enterotoxigenic Escherichia coli. Weaned pigs (n = 34, 6.88 ± 1.03 kg body weight [BW]) were individually housed in disease containment rooms and randomly allotted to one of the three dietary treatments: nursery basal diet (CON) and two additional diets supplemented with 0.5 or 50 mg/kg carbadox to the nursery basal diet (TRA or REC), respectively. The experiment lasted 18 d with 7 d before and 11 d after the first E. coli inoculation. The E. coli F18 inoculum was orally provided to all pigs with a dose of 1010 colony-forming unit (CFU)/3 mL for three consecutive days. Fecal and blood samples were collected on day 0 before inoculation and days 2, 5, 8, and 11 postinoculation (PI) to test the percentage of β-hemolytic coliforms in total coliforms and complete blood cell count, respectively. Sixteen pigs were euthanized on day 5 PI, whereas the remaining pigs were euthanized at the end of the experiment to collect the jejunal and ileal mucosa and mesenteric lymph node for gene expression and bacterial translocation, respectively. Pigs in REC had greater (P < 0.05) final BW and lower (P < 0.05) overall frequency of diarrhea compared with pigs in the CON and TRA groups. Pigs in TRA had the lowest (P < 0.05) average daily gain and feed efficiency from day 0 to 5 PI, highest (P < 0.05) percentage of β-hemolytic coliforms in fecal samples on days 2 and 5 PI, and greatest (P < 0.05) bacterial colonies in mesenteric lymph nodes on day 11 PI compared with pigs in the CON and REC groups. Pigs in TRA had the greatest (P < 0.05) neutrophils on day 5 PI and higher (P < 0.05) white blood cell counts and lymphocytes than other groups on day 11 PI. Pigs in TRA had the greatest (P < 0.05) serum C-reactive protein on days 2 and 5 PI and serum tumor necrosis factor-α on day 5 PI, compared with pigs in the CON and REC groups. Pigs fed REC had increased (P < 0.05) mRNA expression of zona occludens-1 (ZO-1) and occludin (OCDN) and reduced (P < 0.05) interleukin-1 beta (IL1B), interleukin-6 (IL6), and tumor necrosis factor-alpha (TNFA) in ileal mucosa on day 5 PI, compared with the CON, whereas TRA upregulated (P < 0.05) mRNA expression of IL1B, IL6, and cyclooxygenase-2 (COX2) in the ileal mucosa on day 11 PI, compared with the REC. In conclusion, trace amounts of antibiotic may exacerbate the detrimental effects of E. coli infection on pig performance by increasing diarrhea and systemic inflammation of weanling pigs., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The study was conducted to investigate the efficacy of a probiotic Bacillus subtilis strain on growth performance, diarrhea, systemic immunity, and intestinal health of weaned pigs experimentally infected with an enterotoxigenic Escherichia coli and to compare the efficacy of B. subtilis with that of carbadox. Weaned pigs (n = 48, 6.17 ± 0.36 kg body weight [BW]) were individually housed in disease containment rooms and randomly allotted to one of four dietary treatments: negative control (NC, control diet without E. coli challenge), positive control (PC, control diet with E. coli challenge), and supplementation of 50 mg/kg of carbadox (antibiotic growth promotor [AGP]) or 2.56 × 109 CFU/kg of B. subtilis probiotics (PRO). The experiment lasted for 28 d with 7 d before and 21 d after the first E. coli inoculation. Fecal and blood samples were collected on days 0, 3, 7, 14, and 21 post inoculation (PI) to analyze β-hemolytic coliforms and complete blood cell count, respectively. Diarrhea score was recorded daily for each pig to calculate the frequency of diarrhea. All pigs were euthanized at day 21 PI to collect jejunal and ileal mucosa for gene expression analysis. Pigs in AGP had greater (P < 0.05) BW on days 7, 14, and 21 PI than pigs in PC and PRO groups. Supplementation of PRO enhanced pigs' BW on day 21 PI compared with the PC. Escherichia coli F18 challenge reduced (P < 0.05) average daily gain (ADG) and feed efficiency from day 0 to 21 PI, while supplementation of carbadox or PRO enhanced ADG and feed efficiency in E. coli F18-challenged pigs from day 0 to 21 PI. Pigs in AGP and PRO groups had reduced (P < 0.05) frequency of diarrhea throughout the experiment and fecal β-hemolytic coliforms on day 7 PI than pigs in the PC. Pigs in PRO had greater (P < 0.05) gene expression of CLDN1 in jejunal mucosa than pigs in the PC. Supplementation of carbadox or PRO reduced (P < 0.05) the gene expression of IL6 and PTGS2 in ileal mucosa of E. coli-infected pigs compared with pigs in the PC. Pigs in the PRO group had lower (P < 0.05) white blood cell number and neutrophil count, and serum haptoglobin concentration on day 7 PI, and less (P < 0.05) monocyte count on day 14 PI, compared with PC. In conclusion, supplementation of probiotic B. subtilis could enhance disease resistance and promote the growth performance of weaned pigs under disease challenge conditions. The potential mechanisms include but not limited to enhanced gut barrier integrity and local and systemic immune responses of weaned pigs., (© The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)