Alterations In Rumen Microbiome,plasma And Milk Metabolome In Dairy Cows With Milk Fat Depression

Milk fat depression(MFD)is a serious problem in large-scaled dairy farm.Scholars currently believe that MFD is a classic example of the interactions between dietary nutrients,the gastrointestinal microbiota,energy balance,and physiological status.The present study investigated the alterations in rumen microbiome,plasma and milk metabolites composition.We attempted to reveal the causes and mechanisms of MFD in dairy cows based on omics technology.The research content is mainly divided into three parts:1.Studies on alterations in rumen fermentation,plasma biochemical indexes,and milk fatty acids profile in dairy cows with milk fat depressionThe objective of this study was to establish an experimental model of milk fat depression(MFD)of dairy cows and reveal the alterations of ruminal fermentation parameters,plasma biochemical indexes,and milk fatty acids profile in response to MFD in dairy cows.Twelve healthy Holstein dairy cows(second parity,similar body weight)were randomly assigned into a control(CON)group and a treatment(TR)group(n=6 in each group).Cows in TR group received a high-starch total mixed ration(TMR)designed to induce an MFD physiological state,while cows in CON group received normal TMR.Diet,milk,and plasma samples were collected on the 51st,52nd,and 53rd day of the experimental period.Ruminal fluid samples were collected on the 54th and 55th day of the experimental period.Results showed that the milk fat yield(P<0.001)and concentration(P=0.001)significantly decreased in TR group cows compared with CON group cows.Rumen fermentation parameters results revealed that ruminal pH(P=0.011),acetate proportion(P=0.005),butyrate proportion(P=0.018),and acetate to propionate ratio(P=0.001)were lower in TR group than CON group.The concentration(P=0.002)and proportion(P<0.001)of propionate were higher in TR group than CON group.Plasma biochemical indexes results revealed that compared with CON group,the glycerol(P=0.013)and non-esterified fatty acid(NEFA)(P=0.004)concentrations were decreased in TR group.Milk fatty acids composition results revealed that C6:0(P=0.001),C14:0(P=0.028),C16:0(P=0.002),and C18:0(P=0.024)concentrations in TR group were lower than CON group.In addition,cis-9 C16:1(P=0.032),trans-11 C18:1(P=0.012),and cis-11 C20:1(P=0.019)concentrations in TR group were lower than CON group.In general,pelleted high starch diet could induce MFD in dairy cows.Some milk short chain fatty acids,mono-unsaturated fatty acids and plasma NEFA concentrations were decreased,rumen fermentation type was changed to propionate fermentation.2.Studies on alterations in rumen microbiome and metabolome in dairy cows with milk fat depressionThe objective of this study was to investigate the ruminal microbiome and metabolome alterations in response to milk fat depression(MFD)in dairy cows.The experimental design was same to chapter 2.Ruminal fluid samples were collected on the 54th and 55th day of the experimental period.Results revealed that the structure of microbial flora tends to be simplified.At the phylum level,TR group cows had a higher relative abundance of Bacteroidetes(P=0.018),with a lower relative abundance of Firmicutes(P=0.028)and Proteobacteria(P=0.006)than CON group cows.At the genus level,TR group diet increased the relative abundance of Prevotella(P=0.018),decreased the relative abundance of unclassfied Lachnospiraceae(P=0.045),Oribacterium(P=0.010),Pseudobutyrivibrio(P=0.010),and unclassfied Veillonellaceae(P=0.011)compared with CON group diet.Metabolomics analysis revealed that the ruminal fluid content of amino acids(glutamine(FDR=0.035),isoleucine(FDR=0.043),and alanine(FDR=0.046)etc.)and amines(N-acetyl-beta-D-mannosamine(FDR=0.043),malonamide(FDR=0.043),5-methoxytryptamine(FDR=0.045),and indole-3-acetamide(FDR=0.035))were significantly increased in TR group cows compared with CON group cows.Correlations between microbiome and metabolome analysis revealed that levels of amines and amino acids were negatively correlated with the abundance of Oribacterium,Pseudobutyrivibrio,RC9_gut_group,unclassfied BS11_gut_group,and Selenomonas(P<0.05,|r|>0.75).In general,the composition and structure of rumen microbiota were changed under the condition of MFD in dairy cows.In addition,some inflammatory substances in rumen fluid were significantly increased,indicating that the rumen microbiota and metabolic disorders in dairy cows.3.Studies on alterations in plasma metabolome in dairy cows with milk fat depressionThe objective of this study was to investigate the plasma fatty acids profile and metabolome alterations in response to milk fat depression(MFD)in dairy cows.The experimental design was same to chapter 2.Plasma samples were collected on the 51st,52nd,and 53rd day of the experimental period for metabolome and fatty acids profile analysis.Results revealed that C16:0(P=0.017),trans-9,12 C18:2(P=0.014),and trans-10,cis-12 C18:2(P=0.038)concentrations were higher,while the C18:0(P=0.013),cis-10 C15:1(P=0.009),cis-9 C18:1(P=0.019),cis-11 C20:1(P=0.001),cis-13 C22:1(P<0.001),and trans-11 C18:1(P=0.003)concentrations were lower in TR group than CON group.Plasma metabolomics analysis revealed that the differential metabolites were mainly belonged to organic acids(alpha-D-glucosamine-1-phosphate and fumarate,etc.),amino acids(glycine,isoleucine,and leucine,etc.),sugar alcohols(myo-inositol,etc.),and lipids(methyl palmitoleate,etc.).In general,these findings demonstrated the shifts of plasma fatty acids profile in MFD cows.In addition,the amino acids and lipids metabolism were changed,which were closely related to MFD syndrome.