Microbial Diversity And Metabolomics Studies On Milk During Bovine Mastitis

Bovine mastitis is one of prevalent diseases in dairy cows and brings huge economic losses to the dairy industry worldwide. In this study, all milk samples were collected from Holstein cows at Enhe dairy farm in Hohhot, Inner Mongolia. According to the SCC, milk samples were divided into 3 groups, healthy milk samples, subclinical mastitic milk samples and clinical mastitic milk samples. The PCR-DGGE and UPLC-Q TOF-MSE technology were applied to analyze the changes in microbiota community structure and metabolites of milk during bovine mastitis.The result of microbial diversity showed that the bacterial and Ciliates’composition of clinical mastitic milk were more complicated than those of healthy milk. However, the number of bands in DGGE profile and Shannon-Wiener index of Lactobacillus were significantly lower than those of healthy milk. And PLS-DA diagrams also clearly showed that the microbial community structure of clinical mastitic and healthy milk had significant difference, which is in accordance with the results of DGGE profiles and UPGMA cluster analysis. Besides, the bacteria associated with clinical mastitic milk were Escherichia coli, Streptococcus agalactiae and Streptococcus; the bacteria associated with healthy milk were Lactobacillus and Bifidobacterium. All of those inferred that Lactobacillus may play an important role in protecting cows from being inflected by pathogenic bacteria.Based on PCA and OPLS-DA, the result of milk metabolites showed that clinical mastitic, subclinical mastitic and healthy milk metabolites had significant difference. Moreover, compared to healthy milk samples, D-glycerol 1-phosphate, citrate, glucose, 4-hydroxyphenyllactic acid, phosphocholine, malate, L-carnitine, hippurate and other 14 metabolites were decreased in clinical mastitic milk samples, whereas valine, isoleucine, proline, arginine and small peptides were increased. And O-propanoyl-carnitine, D-glycerol-1-phosphate, benzoic acid, L-carnitine, aconitate and other 9 metabolites were decreased in subclinical mastitic milk samples compared with healthy milk samples, whereas arginine and small peptides were increased. Besides, in the clinical mastitic milk samples, the relative concentration of 4-hydroxyphenyllactic acid, aconitate, lactose and other 9 metabolites were found to be lower than these in the subclinical mastitic milk samples, whereas small peptides was higher than that in the subclinical mastitic milk samples. Meanwhile, the main metabolic pathways involved contain TCA circle, glycerophospholipid metabolism, carnitine metabolism, peptides, tyrosine, phenylalanine and arginine metabolism.In summary, the microbial community structure and global metabolite changes significantly during bovine mastitis. And, it inferred that milk microbial structure is closely associated with milk metabolites. Different microbial community structure contribute to different milk metabolites to a certain extent.