Ketosis in dairy cows is often accompanied or secondary to mastitis, fatty liver, postpartum paralysis, endometritis, pregnancy toxemia, etc. Through the analysis of cow disease images with B-ultrasound, most of the ketosis in dairy cows is accompanied by a peripartum disease. This is because on the one hand, the occurrence of ketosis reduces the resistance of dairy cows to diseases, and the probability of suffering from other diseases increases through B-ultrasound observation; on the other hand, the occurrence of other diseases in the peripartum period will lead to decreased appetite, and the probability of secondary ketosis will also increase greatly. Experiments have shown that the occurrence of fatty liver often precedes the occurrence of clinical ketosis, which is often due to many functional disorders when dairy cows suffer from fatty liver first, and then suffer from ketosis after a long time. The lack of minerals such as cobalt, iodine, and phosphorus in feed, various stress factors and other endocrine disorders can also promote the occurrence of ketosis. Cows with ketosis have a short-term negative effect on the immune system. The analysis of B-ultrasound data shows that cows with ketosis are generally more likely to suffer from severe mastitis than healthy cows, which may be mainly related to the damage of the cow's defense system by ketosis. Many researchers believe that in the early stage of infection, the white blood cells of both infected and normal cows play a role, but the white blood cells of cows with ketosis respond very insensitively, which may be a link in the immune response of cows, which may be the reason why newly calved cows are prone to E. coli mastitis; and it is worth noting that when the herd as a whole has ketosis, newly calved cows are more susceptible to severe mastitis. Bo Xianglai reminds farmers to treat dairy cow ketosis correctly and use cow B-ultrasound machines to observe whether they are suffering from mastitis and other diseases at the same time.