Skip to main content

What is Recombinant Bovine Somatotropin (rbST or bST)

milk label

The use of recombinant bovine Somatotropin (rbST or bST) was approved in 1994 by the FDA (Federal Drug Administration) for use in lactating dairy cattle. rbST is a naturally occurring protein hormone produced in the pituitary glands of ALL cattle, including those raised to organic, all-natural, or grass-fed standards. bST is one of the hormones in cattle that is responsible in normal growth and development of the mammary gland and milk production. The presence of bST in cow’s milk is normal and natural!

How does bST increase milk production?

During supplementation with bST, the cow’s mammary gland takes in more nutrients from the bloodstream producing more milk. To support this, the cow will consume more feed and water during the supplementation process. Cows generally do not receive bST for their entire lactation period, instead it is only used after peak lactation times and before they enter their dry period. The administration of bST has been shown to increase milk production by an average of 10 - 15 pounds per cow, per day over the lactation period, or as long as the bST supplementation occurs.

What is the effect of rbST on humans?

rbST is species specific meaning that it will only work on its own kind (other cows in this case). With that in mind, growth receptors in the human body do not recognize bST, and it will not trigger a growth response. The hormone bST is a protein, not a steroid, so it is biologically inactive in humans; and can be harmlessly digested in the human stomach like other proteins. In addition, 90% of rbST and bST is destroyed during the pasteurization process. Remember, ALL cow’s milk has always contained small amounts of bST – as it is naturally occurring.

How is bST milk labeled?

The FDA has banned the dairy industry from labeling products as “bST free” since bST is naturally occurring. The labeling “bST free” violates the truth in labeling provisions of the federal law. In addition, persons against bST supplementation believe that products from cows treated with bST should be labeled. However, the U.S. food labeling law says that the presence of an ingredient or substance may be identified on a package label only when that ingredient or substance changes the food from its natural state. Since supplemented bST is indistinguishable from naturally occurring bST (even at the molecular level), the FDA ruled that milk from supplemented cows is not different from milk produced by non-supplemented cows.

rbST General Information, Cornell University
bST and Milk, North Carolina State University Cooperative Extension
Recombinant Growth Hormone, American Cancer Society
What Is rbST and How Does It Work?, Global Dairy Innovation 

By Lindsay Chichester, UNL Extension Livestock Educator