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About 17 percent of all cows in the U.S. are treated with recombinant bovine growth hormone (rBGH). The safety of this product is based on a single 90-day study on rats. Although approved and defended by the Food and Drug Administration (FDA), the pros and cons of rBGH remain hotly debated between large biochemical companies and the dairy industry on one side, and animal rights and food safety advocates on the other.


Recombinant bovine growth hormone is an artificial, lab-synthesized version of the natural hormone bovine somatotropin. Created by Monsanto using recombinant DNA technology, rBGH was first marketed as Posilac in 1994 after FDA approval. The synthetic hormone is referred to in the literature as rBGH, as recombinant bovine somatotropin (rBST), or simply as artificial growth hormone. The dairy industry defends the use of rBGH because it increases the milk yield of cows, but others are concerned by the health risks posed both to the animals and to humans who consume the milk.

More Milk

Use of rBGH increases milk production in cows by about 11 percent, and in some cases by up to 40 percent. This is the primary benefit associated with using rBGH; the increased production allows farmers either to sell more milk or own fewer cows, both of which lead to higher profits. Proponents of rBGH, including Monsanto and the FDA, assert there is no difference between milk produced by cows receiving rBGH and milk from cows that are not.

Risks to Animals

Even if the milk produced is identical, there is evidence that the use of rBGH poses significant risks to the animals themselves. A meta-analysis of several studies, published by the Canadian Veterinary Medical Association, showed that while cows consumed more food daily while on rBGH, they nevertheless lost weight and displayed decreased overall health. A similar study by the European Union's Scientific Committee on Animal Health and Animal Welfare also found an almost 25 percent increase in the incidence of mastitis (an inflammation of the udders), a 40 percent reduction in fertility and a 55 percent increase in risk of lameness.

Risk to Humans

Risks of rBGH to humans are also asserted, but more difficult to prove. The FDA maintains that any rBGH transferred in milk to humans poses no risk because of the low levels of exposure. Claims that milk from rBGH-treated cows contains higher levels of insulin-like growth factor-1 (IGF-1), which has been linked to colon and breast cancer in humans, remain controversial. Several studies, summarized in a report prepared for the Joint Expert Committee on Food Additives, have shown that IGF-1 in milk can survive digestion in the stomach and be absorbed in the small intestine.

The Milk

Monsanto maintains that the milk produced by cows treated with rBGH is indistinguishable from other milk after pasteurization. Nevertheless, opponents to the use of rBGH, like Sustainable Table, point to the bleeding and secretion of pus resulting from mastitis in treated cows as a significant adulteration of the milk produced with rBGH. That pasteurization reduces the health risks of this foreign matter does not make it more appealing to many consumers: The European Union, Japan, Australia and Canada have banned the use of rBGH due to both animal and human health concerns.