Recombinant bovine somatotropin (rBST) is a hormone used by many commercial dairies to increase milk production. The hormone has been marketed under a number of names, but most consumers know it as rBST or BST. The use of rBST has met with some controversy from a variety of fronts, including the animal rights movement and some commercial dairy farmers. As a result, dairies that produce milk products without the use of rBST have begun indicating this on their labels.

After some battling with the United States Department of Agriculture, dairies in the United States are allowed to use the rBST free label as long as a disclaimer is included suggesting that no harmful human health effects have been linked with the hormone. This claim is contended by some scientists, who argue that further research on the hormone is needed. However, there is some agreement within the commercial dairy industry that the use of rBST is harmful to the cows, forcing them to produce more milk than they can safely do normally. As a result, cows treated with rBST have been found to develop bone weakness and usually die within one or two milking cycles of rBST treatment.

Because of this, the use of rBST is usually reserved for cows who have already reached the end of their lives, in an attempt to extract more milk from them. These cows may have a difficult end of life, with some experiencing broken limbs due to calcium deficiency because their excessive milk production has stripped the calcium from their bones. These cows may also be undernourished, because all of the energy they derive from food goes into milk production.

With growing consumer awareness of farming practices, dairies have begun to realize that treating their cows more humanely may result in a stronger and more loyal customer base. Because rBST can express in milk, dairies also want consumers to know that their milk products do not contain the hormone, so that consumers can make their own choices about whether or not to consume it. The use of the rBST free label has been bitterly fought by both pharmaceutical companies and major dairies, who would prefer that the label not be used at all.

rBST is actually a natural hormone that can be found in the pituitary glands of all cows. Research discovered that cows with elevated levels of the hormone produced more milk, and that rBST extracted from one cow and injected into another would result in higher levels of milk production for the rBST treated cow. In the 1980s, synthesized rBST was developed, and testing began in dairy cattle. The United States Department of Agriculture determined that because rBST is a species specific growth hormone, milk from rBST treated cows is identical to that of cows not injected with the hormone. As a result, rBST treated milk was approved for commercial sale.

Many nations, including those in the European Union and Canada, have banned the use of rBST in their cattle. The European Union is more inclined to ban the use of hormones in their food supply, suggesting that they would prefer that consumers eat more naturally produced foods. Many advocates against the use of rBST point to this ban, suggesting that the United States should follow suit and disallow the use of the controversial hormone.