Monsanto, the developer of rBST (PosilacĀ®), stated in its July 16, 2009 publication "Milk Labeling - Is Monsanto Opposed to Truth in Labeling?," available at the Monsanto website:

“Monsanto’s rBST product, Posilac, is a supplement of the naturally occurring cow hormone BST, that when administered to cows allows them to produce more milk. Many dairy farmers use Posilac because they can produce more milk with fewer cows. The milk from treated cows is identical to milk produced by cows that are not treated. There is no laboratory anywhere in the world that can tell the difference between milk from a cow that has been treated with Posilac and milk from one that hasn’t been treated. Milk from treated cows is just as safe as milk from untreated cows. This has been affirmed by the U.S. Food and Drug Administration, World Health Organization, American Medical Association, American Dietetic Association and regulatory agencies in 30 countries.”

July 16, 2009