Talk about milking an issue. Adding a new twist to the debate over the safety of hormones in milk, a new industry study concludes that injecting cows with a growth hormone known as recombinant bovine somatotropin (rbST) designed to increase their milk production is environmentally friendly. Why? Because it has the potential of reducing the number of greenhouse gas–emitting dairy cows on the planet without decreasing milk production.

"By using rbST, we could produce more or the same amount of milk with fewer cows," says animal nutritionist Judith Capper of Cornell University, co-author of the study published in Proceedings of the National Academy of Sciences USA. "That means less land use, feedstock, nutrients, greenhouse gases, excretion—all positive effects on the environment."

The National Research Council in Washington, D.C., estimates that dairy cows account for as much as 20 percent of human-induced emissions of methane, a potent climate change–causing greenhouse gas.

According to the new study, if U.S. farmers injected their dairy cows with bovine growth hormone, it would take just 843,000 cows to produce the same amount of milk as one million untreated animals, potentially saving 2.3 million metric tons of feed—and therefore 540,000 acres (219,000 hectares) of cropland—as well as reducing the global warming impact by the equivalent of 400,000 cars. Researchers say the treatment would up the milk output of cows by nearly 7 percent, potentially decreasing emissions by about the same amount annually.

Some scientists and consumer advocates, however, are skeptical. The study was conducted with a scientist, Roger Cady, who is also the rbST technical project manager for Monsanto, the Saint Louis–based agricultural giant that manufactures and markets it under the brand name POSILAC. In addition, the lead scientist, nutritional biochemist Dale Bauman of Cornell University, has been a paid consultant for Monsanto since the 1980s, though he declined to disclose how much the company has paid him over the years. He insists that Monsanto did not influence his decision to spend as much as $10,000 in university funds for this study.

There is currently a debate raging over the safety of bovine growth hormone. The U.S. Food and Drug Administration (FDA) in 1993 ruled that it was not harmful and could be injected into cows to improve their milk production. But some studies have linked it with a risk of mastitis (udder infection) in cows, requiring the use of antibiotics that may in turn be contributing to the evolving resistance of bacteria to the drugs.

Bovine growth hormone is also known to stimulate the production of insulinlike growth factor 1 (IGF1) by the liver; some studies have shown that high levels of IGF1 in the bloodstream may heighten the risk of prostate and breast cancers as well as a woman's chance of conceiving twins. As a result of consumer concerns, farmers in Australia, Canada, the European Union and New Zealand do not inject their cows with bovine growth hormone.

Monsanto is currently in the midst of a fight in the U.S. to prevent dairy farmers from labeling their milk as rbST-free or as produced by cows not treated with bovine growth hormone. The company charges that such claims cannot be verified, because there is no inexpensive test to prove that cow milk is free of artificial hormones. At Monsanto's request, several states are weighing new regulations barring such labeling, even though the FDA last year ruled that such labels are neither false or misleading.

Many U.S. dairy farmers have pledged not to use the growth hormone in their products, and corporate milk consumers such as Kraft Foods and retailers such as Wal-Mart have announced plans to shift to dairy products that do not contain artificial hormones.
In addition to conflict-of-interest concerns, critics of the study charge that it was based on a faulty premise. "It all hinges on one notion: that there is an increase in feed efficiency," says biologist Michael Hansen of the Consumers Union, an advocacy group that is leading the fight for labeling and against use of bovine growth hormone. In other words, the study assumes that POSILAC increases the ability of individual cows to produce more milk from the same amount of feed, despite an FDA ruling to the contrary. "If the basic assumption is wrong," Hansen says, "then everything that flows from it is of questionable status."

He notes that the FDA analyzed the environmental impact of POSILAC some 15 years ago (as it assessed its safety) and at that time concluded that it might actually increase greenhouse emissions slightly because of, among other factors, the diesel expended to transport it to farms. But any increase or reduction, the agency said, would be "extremely small and insignificant compared to total worldwide emissions of carbon dioxide and methane."

The National Academy of Sciences and the U.S. Environmental Protection Agency have reached similar conclusions about the potential environmental benefits of bovine growth hormone use, but Bauman—who dismisses charges that his relationship with Monsanto taints the study's findings—says his research was more "rigorous" and detailed.

Dairy farmers, however, have already done a pretty good job of reducing greenhouse gas emissions without resorting to bovine growth hormone: Such emissions from the U.S.'s roughly nine million cows are 70 percent lower than those from a dairy herd of 25 million in the 1940s, thanks to improvements in breeding and nutrition, according to U.S. government statistics. And researchers at the University of Melbourne in Australia say they can be cut by another 50 percent simply by changing cow feed to include more digestible grasses, thereby reducing the methane output.