A Comparative Study Of Blood And Milk Metabolite Differences In Cows With Different Milk Yield

The aim of this experiment was to investigate the differences in production performance,blood metabolome and milk metabolome between high and low milk yield Holstein dairy cows.Based on the metabolomics method of LC-MS,the changes in blood metabolites and milk metabolites components in dairy cows were studied,the physiological differential metabolites were screened,and the relationship between changes in metabolites in blood and milk and lactation in cows were explored.Experiment 1:Study on the blood metabolome of dairy cows with different milk yieldIn this experiment,12 healthy lactating cows with similar parity and days in milk were divided into high yield group and low yield group according to 305d milk yield,with 6 cows in each group.Blood samples were collected from the tail vein and plasma metabolomes were determined by LC-MS nontargeted metabolomic assay technique.The results showed that compared to the low milk yield cows,plasma metabolites of the high milk yield cows had 33 differential metabolites significantly up-regulated and 1 7 differential metabolites significantly down-regulated in the positive ion mode,and 21 differential metabolites significantly up-regulated and 16 differential metabolites significantly down-regulated in the negative ion mode.The significant up-regulation of D-glucosamine 6-phosphate,isocitric acid and sarcosine may be related to the increase of energy metabolism;the significant up-regulation of pyridoxal phosphate and DL-arginine may promote protein synthesis;the up-regulation of blood root base may enhance the immune and antioxidant capacity of the dairy cows,thus improving milk production.The significant upregulation of biotin,nicotinamide,and pantothenic acid in the digestion and absorption pathway of vitamins and 2,6-dihydroxybenzoic acid and catechol(catechol)in the benzoate degradation pathway may promote energy metabolism of high-yield dairy cows and increase their energy supply;the significant upregulation of yridoxal and pyridoxal phosphate in the vitamin B6 metabolism pathway may promote amino acid metabolism and milk protein synthesis in high-yield dairy cows;the significant up-regulation of palmitic acid in the fatty acids elongation pathway may regulate the body’s lipid metabolism and promote the synthesis of milk fat.Experiment 2:Study on the milk metabolome of dairy cows with different milk yieldsThe experimental design was the same as experiment 1.Milk samples were collected in the ratio of 4:3:3 in the morning,midday and evening,and milk composition and milk metabolome were determined.The results showed that compared with cows in the low milk yield group,cows in the high milk yield group had significant lower milk protein rate and the tendency to decrease milk fat rate and no significant difference in lactose rate,but milk protein yield,milk fat yield and lactose yield were highly significantly increased.29 differential metabolites were up-regulated and 19 differential metabolites were downregulated in the positive ion mode;27 differential metabolites were up-regulated and 2 differential metabolites were down-regulated in the negative ion mode.The significant down-regulation of guanidinoacetic acid and arginine in the milk metabolome may be related to the significantly lower milk protein content in the high yield group compared to the low yield group;the significant up-regulation of phytanic acid may have a role in promoting milk fat synthesis in cows.The significant up-regulation of glycine and sarcosine and down-regulation of guanidinoacetic acid in the glycine,serine and threonine metabolic pathway may provide cows with essential energy by reducing the production of guanidinoacetic acid from glycine and increasing the production of glycine from sarcosine,which in turn promotes its production of acetyl coenzyme A.Experiment 3:Association analysis of blood and milk metabolomes in cows with different milk yieldCorrelation analysis of the results of the plasma metabolome and the milk metabolome showed that metabolites such as hippuric acid,allantoin,pseudouridine,deoxythymidine 5’-phosphate,sarcosine and 2,6-dihydroxybenzoic acid were enriched and significantly up-regulated in both the plasma metabolome and the milk metabolome,possibly promoting the synthesis and energy metabolism of milk proteins.In conclusion,the significant changes in differential metabolites in plasma and milk metabolites suggested that high milk yield cows may improve milk production,milk fat yield and milk protein yield by enhancing energy metabolism,amino acid metabolism,glucose metabolism and lipid metabolism.