Protective effect and possible mechanism of arctiin on broilers challenged by <i>Salmonella</i> pullorum

Abstract This study was aimed to investigate the effects of dietary arctiin (ARC) supplementation (100, 200 and 400 mg/kg) on the growth performance and immune response of broilers after a Salmonella pullorum (S. pullorum) challenge, and we conducted in vitro anti-bacterial test to explore the bacteriostatic mechanism of ARC. The in vivo trial was randomly assigned to 6 groups: non-infected control group (NC) and positive control group (PC) received a basal diet; TET group, received a basal diet supplemented with 100 mg/kg chlortetracycline; ARC100, ARC200 and ARC400 groups received a basal diet containing 100, 200, 400 mg/kg ARC, respectively. From d 14 to d 16, all birds (except NC group) were infected with 1 mL (1×10 8 CFU/mL) fresh S. pullorum culture by oral gavage per day. In vivo results showed that dietary supplementation of 200 mg/kg ARC significantly increased average daily gain (P&lt;0.05) and decreased feed-to-gain ratio of broilers versus the PC group during d 15-28 after challenged with S. pullorum (P&lt;0.05). The jejunal crypt depth (CD) were decreased by supplementing 100 or 200 mg/kg ARC in diets compared with PC birds at d 19 (P&lt;0.05). The jejunal villi height (VH) were increased by supplementing 100, 200 or 400 mg/kg ARC in diets compared with PC birds at d 28 (P&lt;0.05). Besides, dietary supplementation of 200 mg/kg ARC increased the jejunal VH to CD ratio (VH:CD) than PC group both at d 19 and d 28 (P&lt;0.05). Notably, the broilers had lower serum lipopolysaccharide (LPS) and diamine oxidase (DAO) levels in the ARC100 and ARC200 groups at d 28 than those in the PC group (P&lt;0.05). Furthermore, in comparison to PC birds, the birds in ARC groups (100, 200, 400 mg/kg) had higher serum contents of IgM and IL-10, and the birds in ARC200 group had higher serum contents of IgA at d 19 (P&lt;0.05). At d 28, the birds in ARC groups (100, 200, 400 mg/kg) had lower serum contents of IL-8, and the birds in ARC200 group had lower serum contents of IFN-γ compared to the PC birds (P&lt;0.05). The in vitro experiment showed that ARC significantly inhibited the biofilm formation and adhesion of S. pullorum (P&lt;0.05). Metabonomics analysis revealed that ARC can restrain the formation of the biofilm by affecting a variety of metabolic pathways of S. pullorum. Therefore, dietary supplementation of 200 mg/kg ARC might be a potentially way to substitute antibiotics to control S. pullorum infection in broilers.