Eucommia ulmoides (Eucommia ulmoides Oliv.) leaf extract alleviates Salmonella pullorum infection in broilers with associated improvements in intestinal tight junction gene expression, permeability markers, and cecal microbiota composition

Salmonella pullorum infection is a major threat to the poultry industry, and the increasing constraints on conventional antibiotic use have created a need for safe and effective alternatives. Eucommia ulmoides ( Eucommia ulmoides Oliv.), a medicinal plant containing multiple bioactive constituents, may offer such an option. In this study, we investigated whether Eucommia ulmoides leaf extract (ELE) could protect chicks against S. pullorum infection. A total of 252 one-day-old broilers were randomly allocated to six groups: an uninfected negative control (NC) group and five groups challenged orally with S. pullorum . Among the challenged birds, one group received no additive (SP), one group was given neomycin sulfate (40 mg/kg) as a positive control (PC), and the remaining three groups were supplemented with ELE at 100 mg/kg (ELEL), 500 mg/kg (ELEM), or 1 g/kg (ELEH). ELE supplementation reduced bacterial colonization in the liver and alleviated the detrimental effects of S. pullorum infection on growth performance and immune organ indices. Histological examination showed that ELE improved intestinal morphology in infected chicks. In addition, serum analyses indicated that ELE decreased the infection-associated increases in diamine oxidase activity and lipopolysaccharide levels, suggesting an improvement in intestinal barrier integrity. Consistent with these findings, ELE attenuated the infection-induced downregulation of tight junction protein mRNA expression, indicating a potential role in preserving epithelial integrity at the transcriptional level. Analysis of the cecal microbiota by 16 S rRNA sequencing further showed that ELE altered the cecal microbial community composition during S. pullorum infection, with changes observed in the Christensenellaceae _R-7_group, Anaerostipes , and Agathobaculum . Overall, ELE attenuated systemic infection, intestinal injury, and growth suppression in S. pullorum -challenged chicks. These effects were associated with improved intestinal barrier-related parameters and alterations in cecal microbial composition, suggesting a potential but not yet confirmed role of the gut microbiota. These findings support the potential of ELE as a prophylactic dietary additive for mitigating the adverse effects of S. pullorum challenge in broilers.