Frequently Asked Questions About rBGH

What is rBST or rBGH?

Bovine somatotropin (BST) is a protein hormone naturally produced in the pituitary glands of cattle. Monsanto developed a recombinant version, rBST, by using a genetically engineered E. coli bacteria. Sold under the brand name “Posilac,” it is injected into cows to boost milk output in the short term. This practice is coming under increasing scrutiny. rBST is also known as rBGH (recombinant Bovine Growth Hormone).

How does rBST affect the animals that receive this drug?

Posilac packaging lists many possible side effects of the drug, including reduced pregnancy rates, visibly abnormal milk, hoof disorders and a need for more drug treatments for health problems. Cows treated with rBST face a nearly 25% increase in the risk of clinical mastitis, a 40% reduction in fertility, and 55% increase risk of lameness. (The Canadian Journal of Veterinary Research, 2003)

Why is increased chance of infections like mastitis a problem?

In addition to the needless suffering of the animal, increased incidence of infections could lead to increased use of antibiotics and an increased risk of antimicrobial residues in milk and to antibiotic resistant bacteria. (“Report on Public Health Aspects of the Use of Bovine Somatotropin,” issued March 15-16, 1999, p.16, and available from The European Commission—Food Safety.)

The United States Centers for Disease Control and Prevention recommend that “Decreasing unnecessary or inappropriate antibiotic use, in humans and animals, will decrease the resistance pressure on the treated organisms. Ongoing efforts. . .are needed. . .so that the efficacy of antibiotics is preserved as long as possible.”

Is rBST allowed for use in other countries?

The product is already prohibited in Canada, Japan, Australia, New Zealand, and in the 27 countries of the European Union.

How does rBST affect milk production?

rBST is known to increase the levels of insulin-like growth factor 1 (IGF-1) in cows, which can lead to increased IGF-1 in milk. (“Report on Public Health Aspects of the Use of Bovine Somatotropin,” issued March 15-16, 1999, and available from The European Commission—Food Safety.)

What are the concerns about IGF-1 in milk?

Many studies have noted some links associated between IGF-1 levels and increased risk of cancer, especially breast and prostate cancer. (Holmes, Pollak, et. al. “Dietary Correlates of Plasma Insulin-like Growth Factor I and Insulin-like Growth Factor Binding Protein 3 Concentrations” Cancer Epidemiology, Biomarkers, and Prevention, Sept. 2002, p. 852-861; Chan, Stampfer, et. al.“Plasma Insulin-like Growth Factor-I and Prostate Cancer Risk: A Prospective Study,” Science, January, 1998, p 563-566; Yu, Jin, et. al, Insulin-like Growth Factors and Breast Cancer Risk in Chinese Women, Cancer Epidemiology, Biomarkers, and Prevention, August 2002, p. 705-712.)

What other potential problems have come up?

Studies of animals exposed to rBST raise concerns about potential changes in milk protein that could lead to allergies. (“Report on Public Health Aspects of the Use of Bovine Somatotropin,” issued March 15-16, 1999, p. 17, and available from The European Commission—Food Safety.)

What do milk and milk product labels need to say about not using rBST?

Labels must be truthful and not misleading. To avoid misleading consumers, Food and Drug Administration (FDA) guidance from February 1994 suggests a label statement such as: “from cows not treated with rbST” or other truthful description.

As recently as August 2007, the Federal Trade Commission (FTC) and FDA rejected a request for new restrictions on rBST marketing claims at the federal level. The FTC stated “food companies may inform consumers in advertising, as in labeling, that they do not use rBST.”