Microarray data analysis of gene expression levels in lactating cows treated with bovine somatotropin

Administration of bovine somatotropin (bST) to lactating cows results in an increase in milk production from 10 to 15%. While physiological mechanisms involved in bST administration are well known, there is limited knowledge about the mechanisms that regulate the bST action at genetic level. For this reason, a microarray experiment was conducted to identify differentially expressed genes when bST is given to milking cows. Sixteen high-density microarrays for cattle, each containing 18,263 gene spots, were used. RNA was extracted from the mammary tissue of four lactating Holstein cows, five and two days before, and one and six days after bST administration. A total of 1,251 and 1,167 differentially expressed genes were detected for mean and median expression intensities, respectively. Only the 115 genes which were identified by both mean and median intensities were taken into account. These genes were grouped into 8 clusters according to changes in expression through time points.