Bovine somatotropin is a peptide hormone that produced in anterior pituitary gland and released under the influence of growth hormone releasing factor. Somatotropin release can be inhibited by somatostatin a 14 amino acid peptide hormone. Since the early 1980s larg amount of highly purified somatotropin have been produced, using recombinant DNA methods. Somatotropin has been short- and long-termeffects on metabolism that booth coordinate and result from its stimulus to milk production. Bovine and human somatotropin (hST) are about 65% homologus and not simillar enough for recombinant bovine somatotropin (rbST) to be active in human if injected. It is unclear that human somatotropin can bind with bovine growth hormone receptors and produce the physiological effects? The goal of this experiment is try to indicate the probable physiological effects of hST in dairy cows.