| Milk fat content is an important index to evaluate the milk performance of dairy cows.Its synthesis process involves the complex biological process of transforming dietary nutrients into milk nutrients through dairy cows,which is affected by diet formula,genetic background,physiological status,rumen microorganisms and other aspects.Rumen microorganisms can degrade the nutrients in the diet by their own enzymes to produce small molecular components,which provide a substrate for the formation of milk fat precursors.Rumen lipid synthesis and metabolism is an important factor affecting the formation of milk fat precursors.To some extent,the transport and metabolic efficiency of lipid metabolites can affect the synthesis process and final yield of milk fat.Under the synergistic effect of rumen microorganisms on the degradation of dietary nutrients and physiological regulation of rumen lipid synthesis and metabolism,the produced precursors are the necessary material basis for milk fat synthesis,and insufficient synthesis of milk fat precursors can cause the decrease of milk fat content in milk.However,there are few reports about rumen microbiome,rumen lipid metabolites,and regulatory network between lipid synthesis and metabolism and milk fat synthesis in dairy cows.Therefore,through the detection and analysis of rumen macro genome,rumen lipid group and plasma lipid group,the potential regulatory relationship between rumen microecology,lipid synthesis and metabolism in vivo and milk fat synthesis in dairy cows was explored.At the same time,through the rumen content transplantation test of low milk fat content dairy cows,the cooperation between rumen microbiome and lipid metabolism was verified The apparent effect of application on milk fat rate.To provide experimental basis for the regulation mechanism between rumen micro ecosystem and milk fat synthesis.After 12 months of DHI data orientation tracking,five cows with high milk fat content(4.1% < milk fat content)were selected as "High MF group",and then five cows with low milk fat content(3.2% < milk fat content < 3.7%)were selected as "Low MF group",and then carry out the following experimental.The difference of rumen fluid and plasma lipid metabolites between the High MF group and the Low MF group were detected by the full quantitative technique of lipomics.After the analysis of the results,it was determined that the main difference of lipid metabolites in rumen fluid included 14 triglycerides and 1 phosphatidylethanolamine.They are: TAG(12:0/12:0/16:1),TAG(12:0/14:0/16:0),TAG(12:0/12:0/18:0),TAG(14:0/16:1/14:0),TAG(12:0/18:1/16:1),TAG(14:0/16:0/16:1),TAG(14:0/16:1/18:1),TAG(14:0/16:0/18:0),TAG(16:0/17:1/18:1),TAG(16:0/17:0/18:1),TAG(16:1/18:3/18:3),TAG(16:0/17:0/18:0),TAG(18:1/18:1/19:0),TAG(19:0/19:0/19:0)and PE(22:5/16:0).The main differential lipid metabolites in plasma include five Phosphatidylcholines and one phosphatidylethanolamine.They are: PC(P-20:0/11:0),PC(P-16:0/18:2),PC(22:4/0:0),PC(17:0/18:1),PC(17:0/20:4)and PE(23:0/18:0).The results showed that the difference of substrate concentration and lactose transport efficiency of milk fat precursors in rumen of dairy cows in High MF group might have a regulatory mechanism for milk fat content.The main differential lipid metabolites in plasma include five Phosphatidylcholines and one phosphatidylethanolamine,which are PC(p-20:0 / 11:0),PC(p-16:0 / 18:2),PC(22:4 / 0:0),PC(17:0 / 18:1),PC(17:0 / 20:4)and PE(23:0 / 18:0),indicating that the differences in fat absorption and transport and the efficiency of lipoprotein synthesis in the plasma of dairy cows in the High MF group may also have a regulatory mechanism for milk fat content.In this study,metagenomics was used to detect the differences of rumen microbial structure and gene function between High MF group and Low MF group.After the analysis of the test results,it was determined that Selenomonas ruminantium,Butyrivibrio proteoclasticus,Butyrivibrio and Veillonella parvula in the rumen of dairy cows in High MF group were significantly increased(P < 0.001),Schizosaccharomyces pombe and Lactobacillus casei were significantly increased(P < 0.05).It was found for the first time that the yield of milk fat may be related to the rumen microorganisms Hyphopichia,Lipomyces and Rhodotorula.The gene enrichment of glycoside hydrolase and carbohydrate binding module in rumen of High MF group was significantly higher than that of Low MF group(P < 0.05);the gene enrichment of fatty acid metabolism,glycerol phospholipid metabolism,fatty acid biosynthesis,sphingolipid metabolism and butyric acid metabolism was significantly higher than that of Low MF group(P < 0.05).The number of GH1,GH2,GH3,GH5,GH16,GH27,GH43,GH51,GH53,GH55,GH67,GH74,GH78 and CBM6 genes in High MF group was significantly higher than that in Low MF group,and the number of GH38,GH116 and CBM3 genes in High MF group was significantly higher than that in Low MF group,among which GH43 was the main enrichment gene;The number of COG0657,COG0318 and COG0304 genes related to lipid transport and metabolism was significantly higher than that of Low MF group,and the number of COG1022 genes was significantly higher than that of Low MF group,of which COG0318 was the main enrichment gene.The difference gene GH43 is mainly encoded by Bacteroidetes,Butyrivibrio and Prevotella,and the difference gene COG0318 is mainly encoded by Proteobacteria and Firmicutes.The difference of these genes and their quantity may be an important factor for rumen microorganisms to degrade dietary nutrients and regulate the production efficiency of milk fat precursors.Based on the integrated analysis of the rumen macro genome and lipid group,the significantly increased selenomonadaceae,butyrivibrio proteoclasticus,veillonellaceae and Aspergillus in the high MF group were determined Fruticulosus and Dictyoglomaceae were positively correlated with TAG(16:0 / 17:0 / 18:0),TAG(16:0 / 17:1 / 18:1),TAG(18:1 / 18:1 /19:0),TAG(19:0 / 19:0 / 19:0)and PE(16:0 / 12:0)(P < 0.05).It is suggested that there is a certain relationship between rumen microbiome and lipid metabolites,which may regulate the synthesis of milk fat precursors.After the contents were transplanted by oral catheterization and rumen gavage,it was determined that the rumen fluid of high milk fat content dairy cows could improve the milk fat rate of low milk fat content dairy cows in a period of time.The results showed that the rumen microecological environment had a direct impact on the apparent milk fat rate of dairy cows.In conclusion,this study comprehensively demonstrated the relationship between rumen microecological environment,lipid metabolism and milk fat production in the same diet structure and feeding environment.The results showed that under the same dietary structure and feeding environment,the main differential lipid metabolites in rumen fluid were triacylglycerol and phosphatidylethanolamine,and the main differential lipid metabolites in plasma were phosphatidylcholine and phosphatidylethanolamine.The difference of relative content of microorganisms with specific functions in rumen plays an important role in regulating the production of milk fat;microorganisms may enhance the metabolism of carbohydrate and lipid substances in rumen by high expression of genes such as GH43 and COG0318,affect the synthesis of milk fat precursors,and have the joint regulation of lipid metabolites in plasma to improve the efficiency of lipid synthesis and metabolism It affects the yield of milk fat. |
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