In order to decipher the amino acid (AA) balance in the dairy cattle with left displaced abomasum (LDA), blood samples were obtained from thirty LDA and 12 healthy control cattle. Plasma from LDA cattle exhibited significantly higher free fatty acid and β-hydroxybutyrate, lower glucogenic AA, such as methionine, alanine and serine, and higher ratio of ketogenic AA among blood free AA, such as leucine and lysine. The Fischer ratio, phenylalanine and albumin were similar to control cattle. These results suggested that LDA cattle were in negative energy balance, but AA metabolism and protein synthesis were within a normal range. Lower glucogenic AA was due to the higher gluconeogenesis, and higher ketogenic AA was due to higher ketogenesis.