Prevalence of subclinical mastitis among dairy cattle and associated risks factors in China during 2012-2021: A systematic review and meta-analysis

Bovine mastitis, especially subclinical mastitis (SCM), is one of the most prevalent and economically costly diseases in the dairy industry worldwide. Understanding the prevalence and spatial distribution of bovine SCM and its associated risk factors will facilitate the prevention and control of the disease. We reviewed published studies pertaining to epidemiological surveys of SCM among dairy cows during the past decade (2012-2021) in China from inception to March 20, 2020, with PubMed, Clinical Trial, VIP, CNKI and databases being used to identify English and Chinese articles. Therefore, we retrieved 41 studies related to epidemiological surveys of SCM among dairy cows, using our eligibility criteria. We demonstrated that the prevalence of SCM in dairy cows was 37.7% during the selected periods, indicating a slight increase in the incidence of SCM in a comparison between 2012 and 2016 and 2017-2021. The estimated prevalence of SCM was 36.4%-50.2% in the seven regions, which was no statistically significant difference. The highest prevalence of SCM was 72% in Inner Mongolia Autonomous Region, and the lowest prevalence was 19% in Hubei Province. The variation in diagnostic methods was not significant in the studies. Dairy cows' parity was a risk factor associated with the prevalence rate of SCM. Cow's age might affect the prevalence of SCM during the selected periods. This study may facilitate the control with specific strategies to reduce costs and antibiotics overuse, enhance food safety and public health.