In lactating dairy cattle, bovine somatotropin (bST) is a naturally occurring species-specific protein hormone and major regulator of milk production. It is produced in the brain and coordinates metabolism to allow more nutrients for milk production. Recombinant bovine somatotropin (rbST) is a synthetic version of bST which is primarily injected into dairy cattle to increase their milk production. Since the 1970’s it has been synthesized in the lab and, in 1993, approved by the FDA as safe for use and for commercial sale. rbST works by increasing milk production in lactating cows and is administrated during week 9 – 10 of the natural lactation cycle (peak) and continued every two weeks until the end of lactation. rbST increases the efficiency of nutrient utilization by keeping milk producing cells alive and active longer, resulting in higher lactation persistency and therefore, a higher milk yield.