Effect Of Dietary Organic Iodine Supplementation On Growth Performance,Immune Function And Intestinal Health Of Meat Ducks Challenged With Avian Pathogenic Escherichia Coli

Iodine is one of the essential trace elements in the body.It can promote the growth of the body and enhance immunity by synthesizing thyroid hormone.As a new type of organic iodine,ethylenediamine dihydroiodic acid(EDDI)has the advantages of high solubility in water,good biological titer and high iodine content.In this experiment,Avian pathogenic Escherichia coli(APEC)(serotype: O78)-infected meat duck was used as a model,and organic iodine EDDI was added to a corn-soybean meal.By investigating the growth performance,immune performance and intestinal health of meat ducks,the alleviation effect of EDDI on ducks infected with Escherichia coli was explored.A 3 × 2two-factor completely randomized experimental design was set up with three levels of organic iodine addition(0,8,16 mg/kg of EDDI were added to the basic diet)and whether APEC was challenged or not,and there were 6 treatment groups,with 6 replicates for each treatment and 10 ducks for each replicate.The feeding period lasted for 20 days.The meat ducks were subjected to the APEC challenge at 7 days,with samples collected on the 9th and 20 th days.The test results were as follows:(1)APEC challenge significantly reduced the BW of meat ducks for 20 days(P <0.05),adding organic iodine to the diet significantly increased the 20 d BW and 7-20 d BWG of meat ducks(P < 0.05).(2)APEC challenge caused fatty degeneration of hepatocytes in liver tissue of meat ducks,necrosis of hepatocytes with a small amount of lymphocyte infiltration,mild edema of epicardium with a small amount of lymphocyte infiltration in heart tissue,16 mg /kg iodine significantly reduced the inflammatory reaction in heart tissue of meat ducks.(3)APEC challenge significantly reduced the contents of total protein,albumin,globulin,alkaline phosphatase,alanine aminotransferase and glutamic-oxalic transaminase in the serum at 9 days of meat ducks(P < 0.05),8 mg /kg iodine significantly increased the level of alkaline phosphatase in the serum at 20 days(P < 0.05).APEC challenge significantly increased the serum TSH level of meat ducks,significantly decreased the serum T3 and T4 levels of meat ducks for 20 days(P < 0.05),the addition of iodine in the diet significantly increased the serum T3 and T4 levels of meat ducks(P < 0.05).(4)Immunity(1)APEC challenge significantly increased the lymphocyte count and hemoglobin concentration in the blood of meat ducks at 9 days(P < 0.05),and significantly decreased the erythrocyte count at 9 days,lymphocyte count and monocyte count at 20 days(P <0.05).Adding iodine to the diet significantly increased the white blood cell count and monocyte count of 20 d meat ducks(P < 0.05).APEC challenge significantly reduced thymus index and bursa index of 9 d meat ducks and thymus index of 20 d meat ducks(P <0.05).(2)APEC challenge significantly increased the contents of Ig A,Ig M,complement C3 and endotoxin in the serum of 9 d meat ducks(P < 0.05).16 mg/kg iodine significantly decreased the levels of serum Ig A,Ig M and endotoxin in 9 d and 20 d meat ducks(P <0.05).(3)AEPC challenge significantly increased the m RNA expression levels of TNF-α,TLR4 and NF-κB in liver and IL-6,IL-1β,TLR4,NF-κB and My D88 in spleen at 9 days of meat ducks(P < 0.05).Organic iodine significantly decreased the expression levels of TNF-α and TLR4 genes in the liver of 20 d meat ducks and the expression level of IL-6 at 9days(P < 0.05).(5)Intestinal health(1)The absolute weight of duodenum at 9 and 20 days and the absolute weight of jejunum and ileum at 20 days were significantly reduced by APEC challenge of meat ducks(P < 0.05).Meanwhile,the relative weight of intestine of meat ducks at 20 days was significantly reduced by APEC challenge(P < 0.05).APEC challenge significantly reduced the absolute length of small intestine in 20 d meat ducks(P < 0.05),and significantly increased the relative length of small intestine in 9 d meat ducks(P < 0.05).AEPC challenge significantly reduced the jejunal villus height(P < 0.05).(2)AEPC significantly downregulated the m RNA expression levels of ZO-2,ZO-3,MUC2 and Claudin1 in the jejunum of 9 d meat ducks(P < 0.05).At the same time,the gene expression of s Ig A in jejunum of 9 d meat ducks increased significantly after AEPC challenge.8 mg/kg iodine significantly increased the m RNA expression level of ZO-3 at 20days(P < 0.05),while 16 mg/kg of organic iodine significantly decreased the m RNA expression level of s Ig A(P < 0.05).APEC challenge significantly increased the m RNA expression levels of IL-1β,TNF-α,TLR4 and NF-κB in jejunum of 9 d meat ducks(P <0.05).Addition of iodine significantly decreased the m RNA expression levels of IL-1β and TNF-α in jejunum of 20 d meat ducks(P < 0.05).(3)At the phylum level,APEC challenge significantly reduced the relative abundance of Firmicutes and Cyanobacteria(P < 0.05),and significantly increased the relative abundance of Bacteroidetes in caecum of meat ducks(P < 0.05).Iodine significantly reduced the relative abundance of Cyanobacteria(P < 0.05).At the genus level,after APEC challenge,the abundance of Alistipes in the cecum of meat ducks increased significantly(P < 0.05),while the relative abundance of Subdoligranulum,Faecalibacterium,Butyricicoccus and Shuttleworthia decreased significantly(P < 0.05).Adding organic iodine significantly increased the relative abundance of Eubacterium coprostanoligenes group and Shuttleworthia in the cecum of meat ducks(P < 0.05).APEC challenge significantly reduced the contents of acetic acid and propionic acid in the cecum of meat ducks(P < 0.05).Iodine significantly increased the contents of acetic acid and butyric acid in the cecum of meat ducks(P < 0.05).To sum up,APEC challenge resulted in decreased immune function and impaired intestinal function of meat ducks,which hindered the growth and development of meat ducks.Adding EDDI to the diet promoted the growth of meat ducks by synthesizing thyroid hormone and improved their disease resistance.By regulating intestinal microorganisms and their metabolites,intestinal health was promoted,and finally the damage caused by APEC challenge on meat ducks was alleviated.