Background

Previous research has shown that dietary supplementation of Bacillus spp. probiotics exerts beneficial effects on animals' growth. However, limited studies have evaluated the efficacy of Bacillus spp. on weaned pigs and their effects on host gut health and microbiome, and systemic immunity using a disease challenge model. The objective of this experiment was to investigate the effects of two Bacillus spp. strains (Bacillus subtilis DSM 32540 and Bacillus pumilus DSM 32539) on growth performance, diarrhea, intestinal health, microbiome, and systemic immunity of weaned pigs experimentally infected with an enterotoxigenic Escherichia coli (ETEC).

Results

Pigs in PRO1 (Bacillus subtilis DSM 32540) had greater (P < 0.05) body weight on d 7 and 14 PI, greater (P < 0.05) ADG from d 0 to 7 and d 7 to 14 PI, compared with pigs in CON (Control). Pigs in PRO1 had milder (P < 0.05) diarrhea on d 2 and 3 PI compared with pigs in CON. However, no differences were observed in growth performance and diarrhea score between PRO2 (Bacillus pumilus DSM 32539) and CON groups. Supplementation of PRO1 decreased (P < 0.05) lymphocyte counts on d 7 and 14 PI, compared with CON. Supplementation of PRO1 and PRO2 both reduced (P < 0.05) total coliforms in mesenteric lymph nodes on d 21 PI. Pigs in PRO2 had greater (P < 0.05) goblet cell number and sulfomucin percentage in duodenal villi and greater (P < 0.05) sialomucin percentage in jejunal villi than pigs in CON. Supplementation of PRO1 up-regulated (P < 0.05) MUC2 gene expression in jejunal mucosa and reduced (P < 0.05) PTGS-2 and IL1B gene expression in ileal mucosa on d 21 PI, compared with CON. Pigs in PRO1 had reduced (P < 0.05) relative abundance of families Lachnospiraceae, Peptostreptococcaceae and Pasteurellaceae in the ileum.

Conclusions

Supplementation of Bacillus subtilis DSM 32540 improved growth performance, alleviated diarrhea severity, enhanced gut health, and reduced systemic inflammation of weaned pigs infected with ETEC F18. Although Bacillus pumilus DSM 32539 was able to alleviate systemic inflammation, it had limited impacts on growth performance and severity of diarrhea of ETEC F18 challenged weaned pigs.

Most of the commercially available β-glucans are derived from yeast, while there are limited research on algae-derived β-glucan in pigs. Therefore, the objective of this experiment was to investigate the influence of dietary supplementation of algae-derived β-glucan on diarrhea, gut permeability, and immune responses of weaned pigs experimentally infected with a pathogenic Escherichia coli (E. coli). Thirty-six weaned pigs (7.69 ± 0.77 kg BW) were individually housed in disease containment rooms and randomly allotted to one of three dietary treatments (n = 12): control diet and 2 additional diets containing either 54 or 108 mg/kg of β-glucan. The experiment lasted 17 d [5 d before and 12 d post inoculation (PI)]. The inoculum used in this experiment was F18 E. coli, containing heat-labile toxin, heat-stable toxin b, and shiga-lie toxin 2. The inoculation doses were 10 10 cfu/3 mL oral dose daily for 3 days. Diarrhea score (1, normal, to 5, watery diarrhea) was recorded for each pig daily to calculate frequency of diarrhea. Blood samples were collected on d 0 before E. coli challenge, and on d 2, 5, 8, and 12 PI to measure total and differential blood cell count in whole blood and several inflammatory markers in serum. Fresh jejunal tissues were collected from 4 pigs in the control group and high dose β-glucan group to analyze gut permeability on d 5 and d 12 PI with Ussing Chamber. Jejunal and ileal mucosa were also collected to measure the mRNA expression of several genes related to gut barrier function and immune responses. Results of this experiment revealed that inclusion of high dose β-glucan reduced (P < 0.05) frequency of diarrhea (29.01% vs. 17.28%) for the entire experimental period. This was likely due to the reduced (P < 0.05) gut permeability and increased (P < 0.05) mRNA expression of gut barrier function genes (Claudin, Occludin, and MUC2) in jejunal mucosa of E. coli challenged pigs as β-glucan supplemented. Supplementation of β-glucan also reduced (P < 0.05) white blood cells, neutrophils, serum tumor necrosis factor (TNF)-α cortisol, and haptoglobin, and down-regulated (P < 0.05) the mRNA expression of several immune genes (IL1B, IL6, and TNFA) in ileal mucosa of E. coli challenged pigs, compared with the control diet. In conclusion, in feed supplementation of algae-derived β-glucan alleviated diarrhea of F18 E. coli infected pigs by enhancing gut integrity. Feeding β-glucan also boosted host immune response against E. coli infection.