ABSTRACT
Bovine somatotropin (bST) is a hormone that is naturally produced in cows' pituitary glands. It is a homeorhetic control that coordinates the metabolism of many tissues in dairy cattle. Recombinant bovine somatotropin (rbST) is a genetically engineered synthetic analog of the natural hormone. Scientists identified the gene responsible for production of the natural bST and, using standard genetic-engineering techniques, duplicated the gene and spliced it into the DNA of E. coli bacteria. The injection of rbST produces a biological reaction that is essentially the same as that which occurs in dairy cows that naturally produce high levels of bST. Critics argue that rbST acts on lactating cells in the mammary gland through a messenger substance called insulin-like growth factor-1 (IGF-1), and that milk from rbST-treated animals contains higher-than-normal levels of IGF-1. Yield trials for dairy cows administered rbST show considerable variability of milk production.
