Effects Of Different Zinc Sources On The Intestinal Epithelial Barrier And Jejunal Mucosal Proteomics Of Newborn Calves Challenged With Escherichia Coli K88

This experiment was conducted to compare the effects of dietary supplementation with low doses of zinc-methionine(Zn-Met)and zinc oxide(ZnO)on growth performance,the incidence of diarrhea,the small intestinal epithelial barrier,and jejunal mucosal proteomics of newborn dairy calves challenged with Escherichia coli K88,which might provide theoretical basis for the application of different zinc sources in calf production.The specific contents are as follows:Experiment 1: The objective of this test was to study the effects of different levels of low-dose zinc oxide on growth performance,diarrhea,immune function and rectal microflora of neonatal Holstein dairy calves.Twenty-four newborn calves were randomly allotted to four groups with 6 calves per group(two female and four male calves).Calves in different treatment was given 0,51.58,103.16 and 154.74 mg ZnO every day(equivalent to 0,40,80 and 120 mg zinc,respectively).ZnO was mixed with milk to feed calves.The trial lasted for 14 days.The results showed that:(1)Different levels of ZnO had no significant effect on the growth performance and diarrhea occurrence of calves(P>0.05),but the ADG and feed intake of calves fed with 80 mg zinc were numerically higher than other groups,and the diarrhea occurrence was the lowest.(2)The serum concentrations of IgG,IgM and IgA of calves increased linearly with the increased dosage of ZnO(P<0.05),and the concentration of ALP tended to increase quadratically(P=0.064).(3)The content of Escherichia coli tended to decrease linearly(P<0.10)and that of Lactobacillus increased linearly(P<0.05)with the addition of ZnO.(4)Considering the experimental results and the limited amount of zinc added,it is better to add 80 mg of zinc to the calf diet.Experiment 2: The objective of this study was to compare the effects of ZnO and Zn-Met on the growth,incidence of diarrhea,and intestinal epithelial barrier of newborn calves challenged with E.coli K88.Twenty-four newborn male calves were randomly allocated to one of three treatment groups: a control group(without Zn supplementation),a Zn-Met supplementation group(receiving 454.96 mg Zn-Met,equivalent to 80 mg zinc),and a ZnO supplementation group(receiving 103.16 mg ZnO,equivalent to 80 mg zinc).ZnO and Zn-Met separately mixed with milk to feed calves.The whole experiment lasted for 14 days.The results showed that:(1)Compared with the control group,Zn-Met significantly increased the average daily gain and feed efficiency and decreased the incidence of diarrhea of calves challenged with E.coli K88(P<0.05).(2)Zn-Met significantly increased ileal villus height,jejunal tight junction protein mRNA expression of Claudin-1,Occludin and ZO-1,and reduced the the concentration of D-lactate in serum of calves infected with E.coli(P<0.05).(3)Compared with control group,duodenal and jejunal villus height,the crypt depth and the ratio of villus height and crypt depth,and the concentration of DAO in serum of calves were not affected by zinc supplement after challenged with E.coli(P>0.05).Experiment 3: The objective of this study was to compare the effects of ZnO and Zn-Met on the jejunal mucosal proteomics of calves challenged with E.coli K88.Experimental design is the same as Experiment 2.Jejunal mucosal samples were collected at the age of 14 days of calves,and the differentially expressed proteins in different groups were analyzed by iTRAQ.The results showed that:(1)Compared with the control group,there were 142 differentially expressed proteins in Zn-Met group,and 133 differentially expressed proteins in ZnO group.(2)Zn-Met upregulated the expression of proteins involved in PPAR signaling pathway,fatty acid metabolism,carbohydrate metabolism,vitamin and mineral element absorption,pancreatic secretion and peroxisome pathway;ZnO promoted the expression of proteins including antigen processing and presentation,phagocytosis,NOD-like receptor signaling pathway,actin cytoskeleton regulation and glycometabolism regulatory pathway.In conclusion,ZnO supplementation improved the immune function,increased the content of Lactobacillus and decreased the content of Escherichia coli in the rectum of calves,and the addition of Zn with 80 mg/d has better effect under the experimental condition.Zn-Met improved growth performance and intestinal epithelial barrier function,and allievated the diarrhea of calves infected with E.coli.Zn-Met promoted the nutriments digestive capacity in jejunal mucosa of calves challenged with Escherichia coli.ZnO enhanced the immune function and energy metabolism in jejunal mucosa of calves.