BST is also known as Bovine Growth Hormone. It is a protein hormone that is produced in the pituitary glands of all cattle, including dairy cows. It occurs naturally in milk. rBST is the acronym for recombinant bovine somatotropin, a synthetic version of BST. Challenge products are made from milk from cows not treated with rBST*.
*No significant difference has been shown between milk derived from rBST-treated & non-rBST-treated cows.