Abstract: [Objective] By analyzing the incidence of cows’mastitis in 381 large-scale dairy farms in 23 provinces from 2018 to 2022,the aim is to analyze the factors that may affect mastitis：month of onset,position and number of affected udder areas,frequency of onset,days in milk（DIM）,parity,severity,etc..[Method] Multiple cases of different DIM in the same parity of each cow were recorded as multiple. The number of cases was counted and summed according to all cows' mastitis events, and the proportion of each level under different factors was subcounted according to the number of mastitis at each level. [Result] Results showed that：（1）The incidence of mastitis was high in July,August,and September.（2）The risk of infection with mastitis in a single udder area was highest,with the left front udder having the highest cumulative incidence,accounted for 27.7%,followed by the right front udder,accounted for 25.3%.（3）Within 14 days after calving,the highest incidence of mastitis was 10.6%,with 43.2% occurring between 0~105 days after calving.（4）After the first onset,26.6% of cows experienced recurrent mastitis（i.e. a recurrence rate of over 25%）,while the third onset accounted for 37.1% of the second onset. When the incidence of mastitis exceeded five or more times,the recurrence rate of cow mastitis exceeded 50%.（5）The cure days for mastitis were mostly in 0~6 days（48.9%）and 7~13 days（31.5%）.[Conclusion] Therefore,to reduce the frequency of mastitis in dairy cows,it is necessary to do a good job in the prevention and reduce cows’mastitis from July to September,strengthen udder care within 14 days after calving,and detect mastitis within 105 days after calving.More observation and care should be conducted in the front udder when cows in the milking palor,and culling cows with frequent mastitis.

Key words: dairy cow, mastitis, incidence frequency, udder