| Early weaning is usually advocated in intensive pig production,and premature weaning is one of the main causes of piglet weaning stress syndrome and diarrhea.In production,high-dose zinc is often used to reduce the occurrence of piglet diarrhea,and zinc is usually added in the form of inorganic zinc such as zinc oxide,zinc sulfate and zinc carbonate.Because the bioavailability of inorganic zinc is very low,which will cause environmental pollution and waste of zinc source.Therefore,the development of organic zinc to replace high-dose inorganic zinc is the focus of current research.Chitosan-chelated zinc prepared in our laboratory is a kind of organic zinc（Chinese patent:201910039700.4）.Chitosan has the characteristics of good biocompatibility,environmental protection and non-toxic.Moreover,due to their special structure of amino and hydroxyl groups,they have strong chelating effects on some metal ions,and the chelates have stronger biological activities,such as stronger antibacterial properties.Preliminary experiments have shown that chitosan-chelated zinc can improve the growth performance and reduce the diarrhea rate of weaned piglets.Since the reduction of diarrhea rate is closely related to intestinal health.The purpose of this study was to investigate effects of chitosan-chelated zinc on ileal and cecal microbial composition,inflammatory response and barrier function in weaned piglets challenged with E.coli K88.1.Effects of chitosan-chelated zinc on intestinal morphology,antioxidant capacity and ileal digestive enzyme activity in weaned piglets challenged with E.coli K88In this chapter,effects of chitosan-chelated zinc on intestinal morphology,antioxidant capacity and ileal digestive enzyme activity in weaned piglets challenged with E.coli K88 were investigated.48 crossbred piglets weaned at 21 d of age were randomly assigned（4 pens/diet;3 pigs/pen）to 4 groups:control group（CON,basic diet）,high dose zinc oxide group（H-Zn O,basic diet supplemented with 1600 mg/kg Zn from Zn O）,chitosan-chelated zinc group（CS-Zn,basic diet supplemented with 100mg Zn/kg and 766 mg/kg chitosan from CS-Zn）and chitosan group（CS,basic diet supplemented with 766 mg/kg chitosan）.On the 15th day of the experiment period,6piglets in each group were randomly selected to be fed with 1010 CFU E.coli K88culture solution,and slaughtered for samples were taken 48 hours later.The results showed that compared with CON group,the ileal villus height and the ratio of villus height to crypt depth were significantly increased in CS-Zn group（P<0.05）,the crypt depth of cecum was significantly down-regulated in CS-Zn and H-Zn O groups（P<0.05）.Compared with the CON,three treatments significantly decreased the content of malondialdehyde（MDA）,increased the activities of glutathione peroxidase（GPX）and total superoxide dismutase（T-SOD）in the ileal and cecal mucosa（P<0.05）.Compared with H-Zn O and CS groups,the ileal and cecal activity of GPX in CS-Zn group was significantly increased（P<0.05）.Moreover,compared with the other three groups,dietary supplementation of CS-Zn can significantly increase the activity of amylase in ileum（P<0.05）,and compared with CON group,the activities of maltase and trypsin in CS-Zn group were significantly increased（P<0.05）,but the effect was not significantly different from that of H-Zn O group（P>0.05）.These results indicate that the supplement of CS-Zn can improve ileal and cecal morphology and structure,relieve oxidative damage of intestinal mucosa,and improve the intestinal function of digestive and absorption.2.Effects of chitosan-chelated zinc on ileal and cecal microbiota and metabolites in weaned piglets challenged with E.coli K88In this chapter,effects of chitosan-chelated zinc on ileal and cecal microbiota and metabolites in weaned piglets challenged with E.coli K88 were investigated.The experimental design was consistent with chapter 1.The results showed that compared with the CON group,theαdiversity index of the ileal contents in the CS-Zn group was significantly reduced（P<0.05）.In addition,both CS-Zn and CS treatments significantly decreased the relative abundance of Proteobacteria in ileal and cecal contents（P<0.05）.The relative abundance of Streptococcus in ileum was significantly decreased in the three treatment groups compared with CON group（P<0.05）.Moreover,CS-Zn and CS treatments significantly increased the abundance of Lactobacillus in the ileal contents,and down-regulated the relative abundance of Actinobacillus（P<0.05）,while the abundance of Lactobacillus in ileum and cecum of H-Zn O group was not significantly different from that of CON group（P>0.05）.Meanwhile,CS-Zn treatment down-regulated the relative abundance of Escherichia＿Shigella and Clostridium in ileal contents（P<0.05）.In addition,CS-Zn treatment up-regulated the relative abundance of Lactobacillus and Prevotella＿9,and down-regulated the relative abundance of Streptococcus and Blautia in cecum（P<0.05）.It was found that the concentrations of propionate,butyrate and lactate in ileum of CS-Zn group were significantly increased,and the p H value in the ileum was significantly lower than that of CON group（P<0.05）.The concentrations of total SCFAs and lactate in cecum of CS-Zn group were significantly increased（P<0.05）,while p H value was significantly decreased.There were no significant differences in the concentrations of total SCFAs,lactate and butyrate between CS-Zn and CS groups（P>0.05）.These results indicate that the supplement of CS-Zn could modulate the composition of ileal and cecal microbiota,increase the concentration of lactate and SCFAs in ileal and cecal contents,which is helpful to maintain a healthy intestinal environment.3.Effects of chitosan-chelated zinc on ileal and cecal inflammatory response and barrier function in weaned piglets challenged with E.coli K88In this chapter,effects of chitosan-chelated zinc on ileal and cecal inflammatory response and barrier function in weaned piglets challenged with E.coli K88 were investigated.The experimental design was consistent with chapter 1.The results showed that the protein expressions of IL-1β,TNF-α,MPO and INF-γin ileal mucosa of CS-Zn and H-Zn O groups were significantly lower than those of CON group（P<0.05）,the concentrations of MPO,IL-1β,TNF-αand INF-γin cecal mucosa of CS-Zn group were significantly decreased（P<0.05）.In addition,the m RNA expression of TLR-4,My D88 and NF-κB in ileal and cecal mucosa were significantly decreased in CS-Zn group（P<0.05）.CS-Zn treatment significantly decreased the relative m RNA expression of Caspase3 in ileal and cecal mucosa（P<0.05）,increased IGF-1 and decreased the Caspase8 in ileal mucosa（P<0.05）.Compared with CON and H-Zn O groups,the relative gene expression of MUC2 in ileal mucosa of CS-Zn group was significantly increased（P<0.05）,the gene expression of MUC2 and MUC4 in cecum of CS-Zn group was significantly higher than that of CON group（P<0.05）.In addition,compared with CON group,the supplement of CS-Zn and CS significantly increased ileal and cecal relative protein expression levels and increased cecal Occludin protein expression levels（P<0.05）.The protein expression level of Occludin in ileum of CS-Zn group was also significantly increased（P<0.05）.These results suggest that the supplement of CS-Zn can inhibit TLR4-mediated NF-κB signaling pathway to reduce inflammation response in ileum and cecum.Moreover,the supplement of CS-Zn improved intestinal barrier function in weaned piglets challenged with E.coli K88 by increasing the expression of intestinal mucin and tight junction protein.The conclusion includes four points:（1）The supplement of CS-Zn improved the ileal and cecal morphology,enhanced intestinal antioxidant capacity,alleviated the intestinal damage caused by E.coli K88 challenge and improved the nutrient digestion and absorption function of ileum.（2）The supplement of CS-Zn can modulate the microbial composition of ileum and cecum,and increase the concentration of SCFAs and lactate in the intestine,which help to maintain a relatively healthy intestinal environment.（3）The supplement of CS-Zn alleviates inflammation response in ileum and cecum by inhibiting TLR4/My D88/NF-κB signaling pathway,and improves intestinal barrier function.（4）By comparing CS-Zn,H-Zn O and CS with the current data,it is concluded that CS-Zn has similar biological effects biological effect as H-Zn O or CS alone in alleviating ileal and cecal inflammatory response and improving intestinal barrier function.In addition,the regulation of CS-Zn on intestinal microbiota and their metabolites may be attributed to the effect of chitosan. |
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