The selective breeding of beef cattle plays an important role in meeting the growing demand for beef and improving production performance. This study used fattened cattle of the Simmental (S) breed, and two crossbreeds: Simmental × Mongolian (SM) and Simmental × Holstein (SH), which were healthy, of similar age and weight. The results showed that the blood glucose (GLU) levels of the crossbred, genetically improved SM and SH groups were higher than that of the S group. Compared with the S group, there were 49 differentially expressed genes (DEGs) in the SM group, of which 18 genes were up-regulated and 31 genes were down-regulated
and 1,031 DEGs in the SH group, of which 251 genes were up-regulated and 780 genes were down-regulated. We found that crossbreeding may increase GLU levels in the blood by upregulating cytochrome C oxidase subunit 3 (COX3) gene expression and downregulating of PRSS2, providing glycogen to the organism, and therefore enhancing GLU-converting capacity. This study highlighted the differences in feed utilization and energy metabolism among crossbred breeds and provides theoretical support for crossbreeding as a means of selecting breeds and improving beef cattle production. However, the expression of the genes were not validated in the present experiments, and these results need further validation.