Effects of two direct-fed microbials on the ability of pigs to resist an infection with Salmonella enterica serovar Typhimurium

Objective: To evaluate the effects of direct-fed microbials (DFMs) containing either Bacillus licheniformis and Bacillus subtilis or Enterococcus faecium on the ability of finisher pigs to resist a Salmonella serovar Typhimurium infection. Materials and methods: Forty finishing pigs were used in a 12-day disease challenge study. Dietary treatments included no DFM (Control; 20 pigs), DFM provided in drinking water (E faecium), or DFM provided in feed (Bacillus). Ten Control pigs were not challenged with Salmonella Typhimurium; the remaining 30 pigs were inoculated on Day 0. Fecal samples were cultured for Salmonella Typhimurium on Days 0 to 5, 9, and 12. Serum haptoglobin (Hp), α₁-acid glycoprotein (AGP), IgG, and IgM concentrations were measured. Pigs were euthanized on Day 12, and tissue and digesta were tested for presence and numbers of salmonellae. Results: Pigs challenged with Salmonella Typhimurium had looser stools (P < .05), greater fecal shedding of salmonellae on Days 2, 3, 4, and 5 (P < .05), and higher serum Hp concentrations on Day 7 (P < .05) than nonchallenged pigs. Serum AGP, IgG, and IgM concentrations were similar between challenged and nonchallenged pigs on all days. Fecal and tissue concentrations of Salmonella Typhimurium and serum Hp, AGP, IgG, and IgM concentrations were similar among challenged groups fed the three dietary treatments. Implications: Under the conditions of this study, DFMs are not effective in reducing prevalence of Salmonella Typhimurium in feces, gastrointestinal contents, or tissues, or decreasing the number of salmonellae shed.