This study evaluated the therapeutic efficacy of Schisandrin A on systemic colibacillosis of chickens. One hundred and eighty, 1-day-old Hailan Brown chickens were divided into 6 groups of 30 chickens each and assigned to the following treatments: 1) uninfected/untreated control; 2) infected
Escherichia coli
; 3) infected-plus low dose of Schisandrin A therapy (50 mg/kg); 4) infected-plus medium dose of Schisandrin A therapy (100 mg/kg); 5) infected-plus high dose of Schisandrin A therapy (200 mg/kg) and 6) infected-plus antimicrobial therapy (florfenicol). Each group of chickens was placed in cages with a photoperiod of 12 h of light and 12 h of dark. Feed and water for all groups were provided ad libitum for the duration of the study. On d 14, all the chickens except the uninfected control group were intraperitoneally inoculated with a fresh culture of
E. coli
containing 1 × 10
8
CFU/mL. The parameters measured included: average daily weight gain (
ADG
), percent survivability, liver index, serum activity of enzymes (ALT and AST), hepatic and intestinal concentrations of TNF-α, IL-1β, IL-6, IL-8, and LPS, expression of tight junction proteins (occludin, ZO-1, and claudin-1), relative abundance of bacterial species and histopathological changes in hepatic and intestinal tissue. The results showed that the medium and high doses of Schisandrin A ameliorated the detrimental effects of colibacillosis on weight gain. Regarding organ indexes,
E. coli
infection induced a significant increase in liver index, all the doses of Schisandrin A produced a significant reduction of liver index in comparison to the
E. coli
infected control. Serum activity of ALT and AST enzymes significantly increased due to
E. coli
infection, with the exception of the low dose of Schisandrin A for AST enzyme activity, all the Schisandrin A treatments significantly lowered enzyme activity in comparison to the
E. coli
infected control. Regarding concentrations of inflammatory markers in hepatic and intestinal,
E. coli
infection caused a significant increase in TNF-α, IL-1β, IL-6, and IL-8, except the lowest dose of Schisandrin A for IL-1β, the rest of the doses tested were able to significantly reduced the concentrations of inflammatory markers. Concentrations of LPS in hepatic and intestinal tissues were significantly increased by
E. coli
infection, all doses of Schisandrin A significantly reduced the concentration of LPS in hepatic and intestinal tissue.
E. coli
infection significantly reduced the expression of 2 tight junction proteins (ZO-1 and Claudin-1), the higher doses of Schisandrin A were effective in significantly increasing the expression of these tight junction proteins when compared with the
E. coli
infected control. Taken together, these results show that...