Abstract: To clarify the pathogens that cause mastitis in cows, the V4-V5 hypervariable region of bacterial 16S rRNA gene in nipple wipes and milk of mastitis cows and normal cows were amplified and high throughput sequenced. The succession of microbial diversity was analyzed by biostatistics. The results showed that there was a very obvious difference in the composition of microbial between the nipple and the milk of the mastitis cow. At the phylum level, the highest abundance was Firmicutes in the nipples, while Proteobacteria was the highest in the milk. All nipples contain Bacteroidetes, while there is almost no in the milk, Fusobacteria only exists in nipples. The microbial community of the nipple and milk after mastitis in cows was different from normal cows. Fusobacteria was only detected on the nipples of mastitis cows, and normal cows were not. The abundance of Staphylococcus on the nipples of mastitis cows was higher than that of normal cows. Enterococcus was detected in mastitis cow milk, but not in normal cows. Therefore, the nipple of the cow was very different from the microbial community in the milk. Microbial composition changes both outside and inside the breast after bovine mastitis. Exogenous pathogens and endogenous sources pathogens can cause mastitis.

Key words: bovine mastitis, nipple, milk, microbial diversity