Effect of a <i>Saccharomyces cerevisiae</i> Postbiotic Feed Additive on <i>Salmonella</i> Enteritidis Colonization of Cecal and Ovarian Tissues in Directly Challenged and Horizontally Exposed Layer Pullets

Determining the efficacy of feed-additive technologies utilized as pre-harvest food-safety interventions against <i>Salmonella enterica</i> may be influenced by factors including, but not limited to, mechanism of action, experimental design variables, <i>Salmonella</i> serovar(s), exposure dose, route, or duration in both controlled research and real-world field observations. The purpose of this study was to evaluate the dietary inclusion of a <i>Saccharomyces cerevisiae</i> fermentation-derived postbiotic (SCFP) additive (Diamond V, Original XPC^®) on the colonization of cecal and ovarian tissues of commercial pullets directly and indirectly exposed to <i>Salmonella</i> Enteritidis (SE). Four hundred and eighty commercial, day-of-age W-36 chicks were randomly allotted to 60 cages per treatment in two identical BSL-2 isolation rooms (Iowa State University) with four birds per cage and fed control (CON) or treatment (TRT) diets for the duration of study. At 16 weeks, two birds per cage were directly challenged via oral gavage with 1.1 × 10⁹ CFU of a nalidixic-acid-resistant SE strain. The remaining two birds in each cage were thus horizontally exposed to the SE challenge. At 3, 7, and 14 days post-challenge (DPC), 20 cages per group were harvested and sampled for SE prevalence and load. No significant differences were observed between groups for SE prevalence in the ceca or ovary tissues of directly challenged birds. For the indirectly exposed cohort, SE cecal prevalence at 7 DPC was significantly lower for TRT (50.0%) vs. CON (72.5%) (<i>p</i> = 0.037) and, likewise, demonstrated significantly lower mean SE cecal load (1.69 Log₁₀) vs. CON (2.83 Log₁₀) (<i>p</i> = 0.005). At 14 DPC, no significant differences were detected but ~10% fewer birds remained positive in the TRT group vs. CON (<i>p</i> > 0.05). These findings suggest that diets supplemented with SCFP postbiotic may be a useful tool for mitigating SE colonization in horizontally exposed pullets and may support pre-harvest food-safety strategies.