Submitted to: Encyclopedia of Dairy Science
Publication Type: Book / Chapter
Publication Acceptance Date: February 16, 2009
Publication Date: January 1, 2011
Citation: Capuco, A.V., Akers, R.M. 2011. Galactopoiesis/Effects of bST. In: Fuquay, J.W., Fox, P.F., McSweeney, P.L.H., editors. Encyclopedia of Dairy Science. 2nd edition. San Diego, CA: Academic Press. p. 32-37.
In the 1930’s and ‘40’s, research demonstrated that a hormone of pituitary origin, growth hormone or somatotropin, increases milk yield of dairy goats and cows. Advances toward understanding the myriad of physiological effects of somatotropin culminated in the concept that somatotropin orchestrates coordinated metabolic responses of tissues throughout the body to regulate nutrient partitioning and enhance milk production, a form of control that has been termed homeorhetic control. With the production of recombinantly derived bovine somatotropin (bST), it became feasible to utilize the hormone for increasing lactational performance of dairy cows. Subsequent investigations and commercial use expanded our knowledge of the physiological effects of bST and demonstrated its efficacy and safety as a stimulant of milk production. Somatotropin appears to be the primary galactopoietic hormone (i.e., hormone that increases milk production) in mammals, except for rodents where prolactin appears to be the primary galactopoietic hormone. Signaling pathways include direct signaling by bST and indirect signaling by insulin-like growth factors (IGFs). Homeorhetic control is exerted in large part by altering the response to homeostatic signals. While bST exerts homeorhetic regulation, homeostatic regulatory processes that ensure animal well-being are still operative, and other homeorhetic mechanisms such as those to support body growth and those to support fetal development during pregnancy are still operative. Thus, bST exerts an overarching control, but not an overriding control, on processes that support milk production.