Mammary glands undergo functional and metabolic changes during virgin,lactation and dry periods.A total of 122 genes were identified as differentially expressed,including 79 up-regulated and 43 down-regulated genes during lactation compared with virgin and dry periods.Gene ontology analysis showed the functional classification of the up-regulated genes in lactation,including transport,biosynthetic process,signal transduction,catalytic activity,immune system process,cell death,and positive regulation of the developmental process.Microarray data clarified molecular events in bovine mammary gland lactation.