Major Causative Bacteria of Dairy Cow Mastitis in the Inner Mongolia Autonomous Region, China, 2015–2024: An Epidemiologic Survey and Analysis

In this study, we sought to evaluate the prevalence of bacterial pathogens of mastitis in dairy cattle in the Inner Mongolia Autonomous Region, China. The study was conducted from 2015 to 2024 using a total of 12,053 clinical mastitis (CM) and sub-clinical mastitis (SCM) samples. The pathogens were isolated and identified by standard bacteriological and mycological methods. The most common pathogens isolated were <i>Escherichia coli</i> (13.82%), <i>Staphylococcus aureus</i> (10.28%), <i>Klebsiella</i> spp. (8.96%), <i>Streptococcus agalactiae</i> (7.45%), <i>Streptococcus uberis</i> (6.60%), <i>coagulase-negative staphylococci</i> (5.84%), and <i>Streptococcus dysgalactiae</i> (4.21%). From 2015 to 2017, the primary pathogens responsible for causing mastitis in cows were <i>Staphylococcus aureus</i> and <i>Streptococcus agalactiae</i>. In 2018, the most frequently isolated pathogen was <i>Staphylococcus aureus</i>. Notably, the isolation rate of <i>Escherichia coli</i> increased from 12.31% to 21.72%, and the isolation rate of <i>Klebsiella</i> spp. increased from 7.52% to 14.01% from 2019-2024. Mycoplasma was only detected in clinical mastitis cases, with a separation rate as high as 6.95%. In summary, the isolation rate of environmental pathogens is gradually increasing, while that of contagious pathogens has been continuously declining. This indicates that the current prevention strategies for infectious pathogens are effective. As a next step, it will be important to develop new strategies specifically targeting environmental pathogenic microorganisms.