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.