Safety of Bovine Somatotropin (bST)

This article will focus on safety. Somatotropin had to be proven safe for humans who consume the milk and meat from animals injected with bST, and it also had to be shown that bST did not cause adverse effects on the health and well-being of the injected cows.

The following information may be useful for you to address concerns of consumers, directors of school lunch programs, dietitians, and other interested parties regarding recent issues about the safety of bovine somatotropin, also called bST or bovine growth hormone.

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Somatotropin is a peptide (a small protein) secreted from the pituitary gland of all mammals, including humans. This hormone controls normal body growth and lactation in many species of animals, as well as affects the metabolism of nearly all classes of nutrients.

Bovine somatotropin has been synthesized using recombinant DNA technology, and a large volume of research from around the world (more than 1,500 studies) has convincingly established that biweekly injections of bST into dairy cows will increase milk production 10 to 15 percent and increase efficiency of feed utilization 5 to 15 percent.

Thus, bST is another useful management tool that can be used to reduce costs to consumers of milk and milk products, making them more competitive in the marketplace. Before bST could be used commercially in dairy cattle in the United States, the Food and Drug Administration (FDA) had to evaluate and rule on its safety, efficacy, and a variety of other issues. The FDA began to address these issues in the 1980s.

This article will focus on safety. Somatotropin had to be proven safe for humans who consume the milk and meat from animals injected with bST, and it also had to be shown that bST did not cause adverse effects on the health and well-being of the injected cows.

By 1994, the FDA ruled that bST was safe for humans and cows and that bST increased milk yield and improved feed efficiency and could be sold for commercial use in lactating dairy cows. Since that time, bST marketed under the trade name of Posilac®, has been used commercially by many dairy farmers in the United States. One basis for the 1994 decision was the finding that oral administration of bST to rats, at doses 100 times or more than the dose administered per pound of body weight daily to dairy cows for up to 90 days, had no effect on cancer incidence, deaths, or other clinical findings. These results supported earlier published research, which showed that bST is biologically inert when consumed orally because it is a peptide and degrades to amino acids in the gastrointestinal tract like any other peptide or protein. Indeed, for any biological activity, bST must be administered by subcutaneous or intramuscular injection or infused directly into the bloodstream.

Furthermore, bST will not evoke a biological response when injected into humans because bST does not bind to the somatotropin receptors in human cells. Such binding is necessary for any biological effect to ensue. In other words, humans will only respond to growth hormone of human or other primate origin, not growth hormone of bovine origin.

There has been speculation that because bST increases concentration of insulin-like growth factor I (IGF-I, another peptide hormone) in milk, it might be linked to a higher incidence of cancer in humans who consume the milk. However, an impressive amount of scientific evidence does not support any link between bST, IGF-I, and cancer.

For example, injection of cows with bST increases concentration of IGF-I in cow’s milk only to levels that approximate those found in human breast milk. Feeding of bovine IGF-I, which is structurally identical to human IGF-I, at very high doses to rats had no biological effects in the test rats. Again, this is what would be expected because IGF-I is a peptide that is rapidly degraded to amino acids in the gastrointestinal tract. Furthermore, humans consume far more IGF-I from swallowing their own saliva each day than from drinking the milk of bST-treated cows.

Another concern has been that bST might increase the incidence of mastitis in cows. It is known that cows producing more milk, regardless of the cause of this greater production, have a small increase in incidence of mastitis. There is a small increase in the cases of mastitis in bST-injected cows. However, this increase is well within the range expected based on the increased milk produced. Furthermore, when calculated on the basis of volume of milk produced, bST does not affect the incidence of mastitis. So the increased incidence of mastitis in cows injected with bST is because of higher yield of milk and not a direct effect of bST.

Since its approval for commercial use, many thousands of dairy cows have been injected with bST, and when used according to label directions, there have been no verified problems. Based on an enormous volume of scientific research and extensive use in the dairy industry, bST is safe for the cow, and the milk she produces is safe for consumers.

In addition to the FDA, the safety of bST has been endorsed by a variety of other scientific and medical organizations, including the American Medical Association, the American Academy of Pediatrics, the National Institutes of Health, the Congressional Office of Technology Assessment, the Endocrine Society Clinical Review, the American Council on Science and Health, a joint expert committee of the World Health Organization, regulatory agencies in more than 30 countries, the American Dietetic Association, the Inspector General of the U.S. Department of Health and Human Services, and the Council for Agricultural Science and Technology.

Author Information

H. Allen Tucker
Michigan State University