Screening Of Antibiotic Substitutes And Improvement Of Immunity And Intestinal Health Of Ducks By Glucose Oxidase

The application of feed antibiotics promoted the rapid development of animal husbandry,while its negative impact is increasingly evident.Banning the use of antibiotics in feed and replacing them has become an urgent problem to be solved in the feed industry.In this study,firstly we established the Escherichia coli(E.coli)attacking model of ducks by preliminary experiment,then selected one feed additive with the best effects of immunity and growth promotion from probiotics,enzymes and plant extracts that have potential to substitute antibiotics,and investigated the effects of the feed additive on immune and intestinal barrier function of ducks infected with E.coli O88 and its mechanism.The first experiment was to screen antibiotic substitutes.Firstly,we established the E.coli attack model of ducks and determined the attack parameters.The 240 1-day-old male lean Peking ducklings were assigned to 5 groups with 6 replications.Ducks were fed a basal diet without or with 30 mg/kg virginiamycin(antibiotic),200 mg/kg Bacillus subtilis(B.subtilis),200 U/kg glucose oxidase(GOD)and 200 mg/kg plant essential oil for 28 d.At day 7,all ducks were orally taken 0.2 mL E.coli O88(3×10~9 CFU/mL)twice,8 hours apart based on the preliminary experiment.The results show that supplementations of the B.subtilis,GOD and plant essential oil improved growth performance of ducks,particularly GOD and plant essential oil have the same effects as the antibiotic.In addition,GOD and antibiotic significantly reduced contents of serum endotoxin and E.coli in ileum of ducks.Therefore,this study selected the GOD as the research object to further explored its mechanism.The second experiment was to investigate the effects of GOD on immune function of ducks infected with E.coli O88.The 144 1-day-old male lean Peking ducklings were assigned to 3 groups with 6replications.Ducks were fed a basal diet without or with 30 mg/kg virginiamycin,200 mg/kg glucose oxidase for 28 d.At day 7,all ducks were orally taken 0.2 mL E.coli O88(3×10~9 CFU/mL)twice,8hours apart.The results show that the addition of GOD reduced serum GLB and TP contents and increased the serum IgG and IgM contents of ducks.GOD reduced the number of red blood cells,and increased the number of white blood cells and lymphocytes proportion.GOD also reduced the contents of MDA and CAT activities in serum,improved serum T-AOC.The contents of TLR4,TNF-α,IL-6 and IL-1βin jejunum of infected ducks were decreased by GOD.It indicated that GOD improved the immune and antioxidant function,and reduced inflammatory reaction of ducks infected with E.coli.The third experiment was to investigate the effects of GOD on intestinal barrier function of ducks infected with E.coli O88.The 144 1-day-old male lean Peking ducklings were assigned to 3 groups with6 replications.Ducks were fed a basal diet without or with 30 mg/kg virginiamycin,200 mg/kg glucose oxidase for 28 d.At day 7,all ducks were orally taken 0.2 mL E.coli O88(3×10~9 CFU/mL)twice,8hours apart.The results show that,supplementation with GOD improved the intestinal morphology of duck by increasing villus height and decreasing crypt depth in jejunum.The GOD decreased intestinal permeability by reducing the concentrations of diamine oxidase and D-lactic in serum of ducks.The GOD maintained intestinal mucosal integrity enhancing the gene expression of tight junction proteins[Claudin-1(CLDN-1)and CLDN-2]and increasing the concentration of sIgA in intestinal mucosa.In addition,GOD increased the number of unique OTUs in the ileum,and balanced the structure of intestinal flora by increasing the relative abundance of probiotics such as Lactobacillales and Bifidobacteriales,and decreasing the contents of E.coli in ileum of ducks.It indicated that the GOD enhanced the intestinal barrier function of ducks infected with E.coli through pathways of physics,immunity and biology.In conclusion,GOD alleviated the adverse effects of E.coli challenge on the ducks by enhancing the immune and intestinal barrier function of the ducks,and improved the growth performance and health of the ducks.GOD can be used as an alternative product of antibiotics to relieve or prevent colibacillosis in ducks.