Comparative Study On Rumen Microflora And Metabolites Of Dairy Cows With Different Yield Levels

Under the same feeding level,there exist significant differences in milk yield between individual dairy cows,which may be closely related to rumen fermentation and microorganisms in addition to genetic factors.Twelve cows with similar age,parity（2-4 parity）and lactation days were selected from 194 cows（average milk yield 48.27 kg/d）in the same enclosure under the same diet condition.They were divided into high milk yield group and low milk yield group according to the milk yield,with 6 cows in each group.Rumen fermentation parameters,apparent digestibility,rumen microflora and metabolome of dairy cows in each group were analyzed and compared,and the test results were as follows:Trial 1:Comparative study on rumen fermentation parameters and nutrient apparent digestibility of dairy cows with different yield levels.The results show that:The concentration of propionic acid in rumen fluid in high milk yield group was significantly higher than the low milk yield group（P<0.05）,and the concentration of isobutyric acid and acetic acid/propionic acid in rumen fluid in high milk yield group were significantly lower than those in low milk yield group（P<0.01）.There were no significant differences in the contents of pH,NH3-N,acetic acid,butyric acid,isovaleric acid,valeric acid and total volatile fatty acid in rumen fluid between high milk yield group and low milk yield group（P>0.05）.The apparent digestibility of EE and NDF in high milk yield group was significantly higher than that in low milk yield group（P<0.05）,and the apparent digestibility of DM,CP and ADF trended to increase（P>0.05）.Trial 2:Comparative study on rumen microflora of dairy cows with different yield levels.The results show that:At the bacterial phylum level,Proteobacteria,Firmicutes and Bacteroidetes were the dominant phyla in the rumen of dairy cows with different yield levels.The relative abundance of Actinobacteria and Planctomycetes in high milk yield group was significantly higher than that in low milk yield group（P<0.01）,and the relative abundance of Spirochaetes in high milk yield group was significantly higher than that in low milk yield group（P<0.05）.Fusobacteria was significantly lower than that in low milk yield group（P<0.01）.The relative abundance of unclassified bacteria was significantly lower than that of low milk yield group（P<0.05）.There were no significant differences in the relative abundance of Proteobacteria,Firmicurium,Bacteroidetes,Patescibacteria,Cyanobacteria,and Euryarchaeota between the two groups（P>0.05）.The relative abundance of unclassified bacteria was significantly lower than that of low milk yield group（P<0.05）.There were no significant differences in the relative abundance of Proteobacteria,Firmicurium,Bacteroidetes,Patescibacteria,cyanobacteria,and Euryarchaeota between the two groups（P>0.05）.At the bacterial genus level,the relative abundance of Candidatus_Saccharimonas and Shuttleworthia in high milk yield group was significantly higher than that in low milk yield group（P<0.01）.The relative abundance of Prevotella₇,Ruminococcaceae_UCG-014 and Ruminococcus₁ was significantly higher than that of low milk yield group（P<0.05）.The relative abundance of Escherichia-Shigella was significantly lower than that of low milk yield group（P<0.01）.The relative abundance of Succiniclasticum and Fusobacterium was significantly lower than that in low milk yield group（P<0.05）.Succinivibrionaceae_UCG-001,Prevotella₁,Ruminococcaceae_NK4A214_group and Rikenellaceae_RC9_gut_group had no significant difference in relative abundance（P>0.05）.At the phylum and genus levels of fungi,there was no significant difference in the relative abundance of each phylum and genus（P>0.05）.Trial 3:Comparative study on metabolomics of rumen fluid of dairy cows with different yield levels.The results show that:Under the positive ion mode,11 different metabolites in rumen fluid of cows in high milk yield group were significantly higher than those in low milk yield group（P<0.05）,and 2 different metabolites were significantly lower than those in low milk yield group（P<0.05）.Under the negative ion mode,10 different metabolites in high milk yield group were significantly higher than those in low milk yield group（P<0.05）,and 3 different metabolites in high milk yield group were significantly lower than those in low milk yield group（P<0.05）.KEGG enrichment analysis showed that rumen metabolites of dairy cows in high and low milk yield groups were significantly enriched in four metabolic pathways,namely Arachidonic acid metabolism,Biosynthesis of vancomycin group antibiotics,Oxidative phosphorylation and Novobiocin biosynthesis.In conclusion,under the same feeding phase,dairy cows in high milk yield group have higher rumen propionic acid content and feed nutrient digestibility.There were significant differences in rumen bacteria at various classification levels between the two groups,but had no significant differences in rumen fungi.Rumen Prevoella,Succinivibrionaceae,Ruminococcus₁,Ruminococcaceae_NK4A214_group and Shuttleworthia cows have positive effects on propionic acid fermentation and NDF digestion in dairy cows.Rumen fluid metabolites Coenzyme Q2 and tyrosine were up-regulated in high milk yield group to promote the growth of rumen microorganisms.