In this study,freeze-drying methods was used to prepare astragalus polysaccharide synbi-otic powder.The optimized freeze-dried protective agent formulation using response surface meth-odology in this study was 17.99％skimmed milk powder,7.26％sucrose,8.04％galactooligosac-charides,and 9.64％astragalus polysaccharide,and the remaining amount was distilled water.The survival rate of lactic acid bacteria in the prepared bacterial powder was 88.06％.A calf feeding ex-periment was conducted over 28 days with thirty healthy newborn calves with similar age,the calves were randomly assigned to either control group and the astragalus polysaccharide synbiotic group,each comprising 15 calves.The astragalus polysaccharide synbiotic group received a supple-ment of astragalus polysaccharide in addition to their regular feed.Compared to the control group,the results showed that:(1)Astragalus polysaccharide synbiotics significantly increased the aver-age daily gain(ADG)of calves and decreased the fecal score and diarrhea rate in calves.(2)By tes-ting the immunological indexes,we found that astragalus polysaccharide synbiotics significantly in-creased the serum level of IgA,IgG,IgM,IL-2 and IL-10,and decreased the level of IL-6 and TNF-α.(3)Astragalus polysaccharide synbiotics notably enhanced the Chao1,Sobs,and Shannon indi-ces,while reducing the Simpson index.At the phylum level,astragalus polysaccharide synbiotics group showed a significant increase in the relative abundance of Cyanobacterium and Firmicutes,and a decrease in Proteobacteria.At the genus level,the relative abundance of Esche-richia-Shigella in astragalus polysaccharide synbiotic group significantly decreased.Whereas norank_f__norank_o__Clostridia_UCG-014 and Butyricicoccus significantly increased.In conclu-sion,this study successfully formulated an astragalus polysaccharide synbiotic powder.The powder can significantly promote the growth of calves,enhance immune function,improve the structure of gut microbiota,and reduce the incidence of calf diarrhea.
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