Bovine somatotropin (bST) is a hormone that occurs naturally in all cows. Its physiological function is to help young cattle grow, and adult cows to produce milk. A small amount of bST is naturally present in all milk, including organic milk.

A synthesized copy of bST – recombinant bovine somatotropin (rbST) – is available for farmers who choose to use the hormone as a farm management tool to boost their herd’s milk production. Health authorities such as the Food and Drug Administration (FDA) and the National Institutes of Health (NIH) have determined that milk from cows treated with rbST is both nutritious and safe.