Recombinant bovine growth hormone (rBGH) or recombinant bovine somatotropin (rBST) refers to bovine growth hormone that is made in a lab using genetic technology. Bovine somatotropin or bovine somatotrophin, or bovine growth hormone, is a peptide hormone produced by cows' pituitary glands. Bovine somatotropin or bovine somatotrophin (abbreviated bST and BST), or bovine growth. Recombinant bovine growth hormones (rBGH), also known as recombinant bovine somatotropins (rBST), are synthetic versions of the naturally occurring peptide hormone made by a cow's pituitary glands. For nearly twenty years, rbGH (recombinant bovine growth hormone), also known as rbST (recombinant bovine somatotropin), has been a staple in the. The Posilac™ product contains a rbGH which is essentially the same as (pituitary derived) bGH.