Effects Of Lactobacillus On Intestinal Flora Andintestinal Mucosal Barrier Of Calf Yak

lactic acid bacteria(LAB)is a kind of probiotics with strong and stable biological effects.Lactic acid bacteria secrete lactic acid as the final product and play an important role in regulating the gastrointestinal flora of animals,maintaining the microecological balance,preventing intestinal bacterial infection,participating in immune regulation,and stabilizing the microbial community.Escherichia coli(E.coli)disease of calving yak is a particularly common disease in the yak breeding industry in Sichuan-Tibet region,with a high fatality rate,which seriously affects the development of the yak industry.The study LAB effects on intestinal flora and intestinal mucosal barrier of calving yak.It is of great significance for the research and development of probiotics to replace antibiotic therapy.In order to investigate the effect of LAB on the prevention and treatment of Escherichia coli disease in calving yaks,24 healthy yaks were randomly divided into 4 groups: control group(group A),model group(group B: E.coli O78 challenge),low LAB group(group C: E.coli O78+ low LAB group),and high LAB group(group D: E.coli O78+ High LAB).After LAB intervention,the composition and functional characteristics of intestinal microflora of the four groups were compared,and pathological sections of small intestine and large intestine tissues of the four groups were analyzed,as well as the expression levels of pathway proteins related to intestinal permeability and apoptoses-related factors.The results are as follows:1.In this study,metagenic analysis was carried out on intestinal microorganisms of calve yak in four groups,and it was found that under different feeding modes,the high-dose LAB group contained more specific bacteria than the low-dose LAB group and the model group,and the uniformity was also higher than the model group.Bacteroidetes,verrucobacteria and Proteobacteria were the dominant phyla in the model group,Firmicutes,spirochetes and actinobacteria were the dominant phyla in the Lactobacillus group,and the relative abundance of Euryarchaea in the model group was significantly higher than that in the Lactobacillus group(P <0.01).There were 13 KOs,95 NOGs and 3 Ca Zs between the model group and the Lactobacillus group(P < 0.05).Compared with the model group,the relative abundance of amino acid metabolism,energy metabolism,classification and degradation,cell motility,cell growth and other metabolic pathways increased in the high-dose lactobacillus group.2.Through the observation and analysis of pathological sections of small intestine and large intestine of calving yaks in the four groups,it was found that compared with the control group,the villus length(VH)of small intestine in the model group was significantly decreased(P < 0.01),and the crypt depth(CD)was significantly increased(P < 0.01).Villus length/crypt depth(V/C)was significantly decreased(P < 0.01).VH was increased significantly(P <0.05)or no significant difference,CD was decreased significantly(P < 0.05)or no significant difference,and V/C was increased significantly(P < 0.05)or no significant difference in low dose LAB group and high dose LAB group.Compared with the control group,the number of goblet cells in the ileum in the model group was less.The number of goblet cells decreased in low-dose LAB group.The goblet cells in the high dose LAB group were similar to those in the control group.No obvious histopathological damage was observed in the cecum and colon of the control group,low-dose LAB group and high-dose LAB group,while epithelial cell necrosis and exhalation and severe inflammatory cell infiltration were observed in the cecum and colon of the model group.3.Western-Blot analysis showed that the expression levels of p38,MAPK and Jnk in small intestine and large intestine of model group were significantly(P < 0.05)or extremely significantly(P < 0.01)higher than those of control group,low-dose LAB group and high-dose LAB group.The expression level of low-dose LAB group was decreased,while the expression level of high-dose LAB group was the lowest,and both showed significant(P < 0.05)or extremely significant(P < 0.01)differences.The expression levels of Bax,Caspase3 in small intestine and large intestine of model group were significantly(P < 0.05)or extremely significantly(P < 0.01)higher than those of the other three groups.The expression level of low-dose LAB group and high-dose LAB group was significantly decreased(P < 0.05)or extremely significantly(P < 0.01).The expression level of Bcl2 protein in small intestine and large intestine of model group was the lowest,with significant(P < 0.05)or extremely significant(P < 0.01)difference.Compared with control group,The expression of Bcl2 protein in low dose LAB group and high dose LAB group showed a trend of significant(P < 0.05)or extremely significant(P <0.01)increase.In conclusion,high-dose LAB had certain effects on intestinal flora composition and function of yak after E.coli O78 challenge,which mainly showed that beneficial bacteria increased and harmful bacteria decreased.At the same time,the high-dose LAB protected the mucosal structure and integrity of the small intestine and large intestine of the calf yak,reduced the damage of the intestinal mucosa,inhibited the expression of the pathway protein related to intestinal permeability and the factor promoting apoptosis,and thus played a role in the prevention and treatment of E.coli O78 induced diarrhea of the calf yak.It provides a certain theoretical basis and experimental basis for the research and development of probiotic products.