Effects Of Astragalus Membranaceus Straw On Rumen Fermentation Parameters,Dry Matter Digestibility And Microflora Of Beef Cattle In Vitro

This experiment was conducted to investigate the effects of Astragalus membranaceus straw on rumen fermentation parameters,dry matter digestibility and microflora of beef cattle in vitro by artificial rumen method,in order to provide theoretical reference for the application of Astragalus membranaceus straw in ruminant production.A single-factor experimental design was used,with 5 treatment groups and 4 replicates per group.In the control group(A0),corn straw was used as fermentation substrate,and in the experimental groups,25%(A25),50%(A50),75%(A75)and 100%(A100)Astragalus membranaceus straw were used to replace corn straw as fermentation substrate,respectively.Rumen fluid of 3 Simmental hybrid fistula cattle(weight about 500±30 kg)was collected for in vitro fermentation.Gas production of each group was recorded at different time points of fermentation and the gas was collected.Fermentation was stopped at 72 h,and the changes of gas composition,p H,ammonia nitrogen,volatile fatty acids and dry matter digestibility of fermentation liquid were measured.Meanwhile,samples of rumen contents were collected,DNA was extracted for PCR amplification,and the changes of rumen microflora were analyzed by sequencing after separation and purification,and protein function and metabolic pathways were predicted by comparison with COG and KEGG.The results showed as follows: 1)Astragalus membranaceus straw significantly increased the gas production and gas production rate in the early and middle stages of rumen fermentation(P<0.05),but there was no significant change in total gas production and gas composition at each time point(P>0.05),but the theoretical maximum gas production was significantly decreased(P<0.01).2)Rumen p H,microbial protein and dry matter digestibility were significantly increased(P<0.05),but there was no significant change in ammonia nitrogen(P>0.05).3)The molar proportion of butyrate,valerate,isobutyrate and isovalerate in rumen was significantly increased(P<0.01);The ratio of acetate to propionic acid,and total volatile fatty acid content were not significantly affected(P>0.05).4)Rumen dominant bacteria and bacteria genera were affected.At phylum level,the relative abundance of Proteobacteria and Desulfurobacteria was increased(P<0.05),but the abundance of Bacteroidetes was decreased(P<0.05).At the genus level,the abundance of Lachnospiraceae＿NK3A20＿group was significantly increased,and the abundance of Papillibacter,Saccharofermentans and Lachnoclostridium was significantly decreased(P<0.01).5)COG comparison predicted that the protein function was mainly concentrated in Function unknown,Translation ribosomal structure,biogenesis,Amino acid transport and metabolism transport and metabolism,Transcription,etc.KEGG database comparison showed that the differential functions were significantly enriched in Metabolism,Environmental Information Processing and Genetic Information Processing and Cellular Processes.The relative abundance of cellular process pathways in A75 and A100 groups was significantly increased(P<0.05).There were 18 secondary metabolic pathways with abundance of more than 1%,which were mainly concentrated in metabolic pathways related to nutrient metabolism and microbial signal transduction and transcription,among which the nucleotide metabolic pathways of Astragalus membranaceus straw groups were significantly decreased(P<0.05).In conclusion,compared with corn straw,Astragalus membranaceus straw can regulate rumen gas production and volatile fatty acid composition,improve rumen p H value,microbial protein and dry matter digestibility.It also increased the abundance of rumen bacteria that degrade substrates such as protein and starch.The differential function of rumen bacteria that in Astragalus membranaceus straw groups was enriched to the genes related to bacterial metabolism and nutrient metabolism related pathways,which enhanced the cellular process pathway and weakened the nucleotide metabolic pathway.In general,Astragalus membranaceus straw has the potential to be used as feed for ruminants.