Abstract: The present study was designed to investigate the therapeutic effect of lytic bacteriophage S13-21 on broilers infected with Salmonella enteritidis, as well as its effect on growth performance, antioxidant capacity, and cytokine and immunoglobulin content. Total of 72 1-day-old AA broilers were randomly distributed into 4 groups with 6 replicates per group and 3 chickens per replicate, namely blank control group (C), Salmonella infection group (S), phage treatment group (S+P) and antibiotic treatment group (S+A). The broilers in groups S, S+P and S+A were infected with Salmonella enteritidis by intraperitoneal injection, and the challenge dose was 200 μL per broiler (1.0×10⁹ CFU·mL^-1). Six hours later, the chickens in groups S+P and S+A were treated by intraperitoneal injection with phage dose of 1 mL per broiler (1.0×10¹² PFU·mL^-1) and antibiotic dose of 200 μL per broiler (gentamicin sulfate, 800 IU per broiler). The treatment lasted for 7 days with an interval of 12 hours. On the fifth day after treatment, broilers were weighed by repetition, and 6 chickens were randomly selected from each group for slaughter. The results showed that:1) At the end of the experiment, the survival rate of broilers in group S was only 59%, compared with group C, the body weight was significantly decreased (P<0.01), and spleen weight increased but the difference was not significant (P>0.05). The activities of T-SOD and GSH-Px in serum and other tissues were extremely significantly decreased (P<0.01), MDA and immunoglobulin content were extremely significantly increased (P<0.01). 2) Compared with group S, the survival rate of broilers in group S+P was increased by more than 25%, and the bacterial load of Salmonella in ileum and cecum were extremely significantly decreased (P<0.01). The contents of antioxidant indexes, cytokines and immunoglobulin in serum and other tissues (except some indexes in ileum) were significantly different from those in S group (P<0.05). In conclusion, Salmonella enteritidis can damage the intestinal mucosal barrier of broilers, resulting in growth retardation, tissue damage and systemic inflammatory response. Phage therapy can specifically eliminate Salmonella enteritidis infection, significantly improve the antioxidant capacity and intestinal mucosal barrier, relieve oxidative stress and inflammatory response, and has a strong protective effect. To a certain extent, it can improve the survival rate and restore the growth of chickens.

Key words: phage, broiler chicken, Salmonella enteritidis, therapeutic effect