| Summary: | Salmonellosis is a zoonotic infection caused by <i>Salmonella enterica</i> serotypes contracted from contaminated products. We hypothesized that competitive exclusion between <i>Salmonella</i> serotypes in neonatal broilers would reduce colonization and affect the host immune response. Day of hatch broilers were randomly allocated to one of six treatment groups: (1) control, which received saline, (2) <i>Salmonella</i> Kentucky (SK) only on day 1 (D1), (3) <i>Salmonella</i> Typhimurium (ST) or <i>Salmonella</i> Enteritidis (SE) only on D1, (4) SK on D1 then ST or SE on day 2 (D2), (5) ST or SE on D1 then SK on D2, and (6) SK and ST or SE concurrently on D1. <i>Salmonella</i> gut colonization and incidence were measured from cecal contents. Livers and spleens were combined and macerated to determine systemic translocation. Relative mRNA levels of interleukin-1β (IL-1β), IL-6, IL-10, IL-18, and gamma interferon (IFN-γ) were measured in cecal tonsils and liver to investigate local and systemic immune responses. When a serotype was administered first, it was able to significantly reduce colonization of the following serotype. Significant changes were found in mRNA expression of cytokines. These results suggest competitive exclusion by <i>Salmonella enterica</i> serotypes affect local and systemic immune responses.
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