Oregano essential oil: a pre-harvest tool to reduce Salmonella enterica serovar Enteritidis in market-age broilers

The objective of this study was to assess oregano essential oil (OEO) as a pre-harvest intervention to reduce Salmonella enterica serovar Enteritidis (SE) colonization in broilers. Two identical floor-pen trials were conducted with a total of 200 Ross 708 straight-run chicks (0 to 43 days). Each trial included 2 pens (50 chickens/pen). All chickens received a common basal corn-soybean meal (C-SBM) diet from 0 to 4 days-of-age and followed a phase-feeding program consisting of starter, grower, and finisher diets to match nutritional requirements. At day 4, pens were assigned to either the basal corn-SBM diet without OEO (control) or the same diet supplemented with OEO (300 g/ton in the feed from 4 to 43 days and 6 oz/gal of stock solution from 28 to 43 days via the water source; Ecodiar®, Nutrinae LLC). At 7 days, chickens were challenged via oral gavage with SE (1 × 10⁵-10⁶ CFU/0.5 mL per chick). At day 43, one cecal pouch per bird was collected for SE enrichment to determine prevalence, and cecal content was analyzed for SE load using standard microbiological procedures. Data were analyzed using Student's t-test, with significance declared at P < 0.05. OEO supplementation reduced SE prevalence from 49% in the control to 34% (P = 0.03). Cecal SE counts were also reduced by approximately 1 log₁₀ with OEO compared with the control (2.7 × 10³ vs. 1.9 × 10² CFU/g; P = 0.02). Mechanistically, OEO supplementation significantly (P ≤ 0.05) reduced protein expression of key inflammatory cytokine (IL-21) and chemokine (MIP-1β) in the cecal tonsil compared to tissue from control-fed chickens. Therefore, OEO supplementation in the feed and water reduced SE prevalence and load in broilers, indicating greater resistance to colonization by reducing inflammation in important lymphoid tissue. This effect may potentially reduce flock-level transmission risk and supports OEO application as a pre-harvest strategy to reduce SE colonization in market-age broilers.