Abstract: Ketosis is a common disease of high-yield cows in early lactation,and classified as clinical ketosis (CK) and subclinical ketosis (SCK) by the clinical symptoms.Ketosis results in an increase of β-hydroxybutyric acid (BHBA) levels in blood and milk.At present,blood BHBA levels are used for the diagnosis of ketosis.CK has a significant impact on the performance of cows,so it attracts the attention of farmers.However,the symptoms of cows suffering from SCK are not obvious and often overlooked by farmers.Like CK and other transition diseases,SCK is also one of the main causes of economic and welfare losses in dairy cows.SCK increases the risk of production-related disorders,such as clinical ketosis,displacement abomasum,retained placenta,lameness,mastitis,and metritis,while reduced animal performance (lower milk production,poor reproductive performance,increased cull rates).SCK may start to affect production even before it is detected,causing huge financial losses in the dairy industry.Notably,the financial losses caused by SCK are more than CK,which are always underestimated by farmers.This review highlights the latest research advances in SCK in dairy cows,which will provide insight into the pathogenesis of ketosis and the adverse effects of SCK on productivity in dairy cows.In addition,early detection and prediction of SCK is presented to decrease the loss of animal welfare and the economy in dairy industry.

Key words: dairy cows; subclinical ketosis; β-hydroxybutyric acid; transition; postpartum diseases