What Is Recombinant Bovine Somatotropin?

Recombinant bovine somatotropin, or rBST, is the synthetic version of bovine somatotropin, or BST. Bovine somatotropin is also known as bovine growth hormone, or BGH, and is produced in the pituitary glands of cattle. RBST is administered to dairy cattle to increase milk production.

History

• Monsanto began researching the effects of BST on dairy cattle in the 1930s. BST was first recovered from the pituitary glands of slaughtered cattle. Concerns of disease transfer led Monsanto to develop a strain of genetically engineered E. coli bacterium. The amino-acid sequence that produces BST is inserted into the bacterium's DNA. Once the E. coli has made sufficient copies of the BST amino-acid sequence, they are separated and the rBST is purified. RBST was introduced in 1994 in the United States and is sold under the name Posilac.

Significance

• The rBST works by delaying mammary cell death and increasing the efficiency of fat-to-energy conversion. Milk is produced cyclically, with milk production at the lowest during the beginning and end of the cycle and peaking near the 70th day of production. RBST is injected into a dairy cow beginning shortly before peak milk production; this allows the cow to produce the maximum amount of milk for the rest of her milk-producing cycle.

Theories/Speculation

• The theory behind rBST is that producing more milk per cow will allow a farmer to care for fewer animals while increasing the amount of milk he sells, which will then increase his profits. However, the consumer backlash has been such that most farmers are not using rBST. Fears of rBST causing human health problems prompted many companies to ban the sale of milk produced by cows injected with it.

Considerations

• The U.S. Food and Drug Administration has found that milk from rBST-treated cows is safe for human consumption, noting that rBST is biologically inactive in humans and that BST and rBST are biologically indistinguishable (see Resources). Milk from treated cows has been found to contain greater levels of IGF-1, a normal growth factor that in excessive amounts has been tied to increased cancer rates in humans, though the FDA says the levels are within the range of those from untreated cows.
  However, animal welfare and human health concerns have prompted Canada, Europe, Australia and New Zealand to ban the sale of milk from rBST-treated cows. Canada, however, allows the sale of dairy products (cheese, ice cream) made from milk produced by rBST-treated cows.

Concerns

• Another concern raised with rBST-treated cattle is an overall decline in their health; rBST-treated cattle are more prone to mastitis, lameness and decreased fertility, according to the Canadian Veterinary Medical Association expert panel (see Resources). Some groups, including Consumers Union (see Resources), have raised concerns that a potential increase in antibiotics to treat cattle mastitis might increase the risk of antibiotic traces reaching consumers or contribute to the growth of antibiotic-resistant bacteria, though the FDA says its safeguards prevent significant levels of antibiotics in milk.