Direct Feeding of Microencapsulated Bacteriophages to Reduce <i>Salmonella</i> Colonization in Pigs

Salmonella shedding often increases in pigs after transportation and/or lairage. We previously showed that administering anti-Salmonella bacteriophages to pigs by gavage significantly reduced Salmonella colonization when the pigs were exposed to a Salmonella-contaminated holding pen. Here we tested whether a microencapsulated phage cocktail would remain effective if the treatment was administered to pigs in the feed. Pigs (n=21) were randomly placed into three groups: feed, gavage, and control. The feed group was direct-fed a microencapsulated phage cocktail daily for 5 days. On the fifth day, the gavage group received the same phage cocktail by gavage, whereas control pigs received a mock treatment containing no phage. All pigs were then orally challenged with Salmonella enterica serovar Typhimurium. Fecal swab samples were collected every 2 h. At 6 h postchallenge, all pigs were euthanized, and ileal and cecal contents and mesenteric lymph nodes were collected and analyzed for the challenge organism. Pigs in the feed group were less likely to shed Salmonella Typhimurium at 2 h (38.1%) and 4 h (42.9%) postchallenge than pigs in both the gavage (2 h: 71.4%; 4 h: 81.1%) and control (2 h: 71.4%; 4 h: 85.7%) groups (p<0.05). Likewise, concentrations of Salmonella Typhimurium in ileal (2.0 log(10) colony forming units [CFU]/mL [contents]) and cecal (2.7 log(10) CFU/mL) contents from feed pigs were lower than ileal (3.0 log(10) CFU/mL) and cecal (3.7 log(10) CFU/mL) contents from control pigs. High concentrations of anti-Salmonella phages were detected in ileal and cecal contents from both feed and gavage pigs (feed ileal: 1.4×10(6); feed cecal 8.5×10(6); gavage ileal 2.0×10(4); gavage cecal: 2.2×10(3)). It is concluded that direct feeding of microencapsulated phages is a practical and effective means of reducing Salmonella colonization and shedding in pigs.