"Genetic engineers develop bovine growth hormone!" Now there's an issue the cartoonists can really milk. Giant cows bursting through the roof of their barns, animals sporting udders from head to tail, scientists peering through microscopes at minuscule cows. Cute, but there is a serious side to the story. A side that impacts on the economics of agriculture, the integrity of an industry, the future direction of science and perhaps even on the health of the consumer.
Way back in the 1930's, researchers discovered that injecting an extract of bovine pituitary glands into lactating cows increased the amount of milk the animals produced. The problem, though, was that the large number of pituitary glands required to prepare the extract made the process impractical. But the 1970's ushered in the era of recombinant DNA technology, and soon the insertion of a gene responsible for the production of bovine growth hormone into E. coli bacteria made the commercial production of this pituitary hormone viable. By the early 1980's experiments involving the bi-weekly injection of BGH, or bovine somatotropin as the substance was also called, were under way in dairy herds. The one unarguable result was that treated cows produced ten to twenty percent more milk. But the consequences of this increased production have been hotly disputed. As a result, Canada has not allowed the use of BGH, but the US has. Contrary to the cartoonists' interpretation, there is no tinkering with the animals' genetic makeup; biotechnology plays a role only in the production of the hormone. BGH is biologically equivalent to the natural hormone which controls lactation, but it is not an exact chemical analogue.
There is no question that some hormone, both in treated and untreated cows, does pass into the milk. This is of no apparent consequence because bovine growth hormone is inactive in humans. In any case, like any other protein, it is broken down in our digestive tract. BGH actually exerts its milk producing effects by triggering the synthesis of a protein known as insulinlike growth factor-I, or IGF-I in the cow's liver. This protein is always present in milk but is found in higher concentrations in the milk from BGH treated animals. These elevated levels are still within the range of variation for untreated milk, and in fact no technology exists that can determine whether a specific milk sample came from a treated or an untreated cow. IGF-I is also a protein hormone, and therefore does not survive the digestion process.
Arguments about possible health consequences of BGH or IGF-I as present in milk are based more on emotion than on science. When BGH was introduced in the US there was one health concern that did seem pertinent. The more milk cows produce, the more likely they are to suffer from inflammation of the udder, a condition known as mastitis. The standard treatment is a course of antibiotics, remnants of which may end up in the milk. Any exposure to antibiotics increases the risk of our developing a resistance to these important drugs and should therefore be limited. But milk is routinely tested and cannot be sold if antibiotic residues are found. Anti BGH activists contend that the testing is inadequate and that not all possible antibiotics are tested for. But BGH has now been in use in the US for years and no increased incidence of mastitis has been noted.
Another question that has been raised deals with the effect of BGH injections on the long term health of cows. There has been some concern that reproductive rates may be affected and activist groups have claimed that the chemical companies promoting the use of BGH聽have suppressed relevant information. Seeing that four major companies are involved in developing the hormone and that thousands of researchers have worked on the project, a cover-up seems unlikely. But even though the loud anti BGH rhetoric is on pretty weak scientific footing, it has had a dramatic impact. Major dairies and supermarket chains have vowed not to accept milk from treated cows, and two school districts, one in California and the other in Wisconsin, have banned such milk from school cafeterias. In California, the stated reason was the concern over safety, whereas in Wisconsin officials claimed that support for the product would be detrimental to small dairy farmers. The widely respected Consumers Union, publishers of Consumers Reports, has also weighed in against the use of BGH. Unnecessary, it claims. We are already awash in milk, with the excess being purchased by the government. However, this really begs the issue. The important point is that whatever amount of milk is required can be produced by fewer cows on less feed with the use of BGH. There could even be an environmental benefit with less nitrogenous waste and less methane being produced.
The bottom line is that the issue is one of attitudes. Many consumers have become distrustful of science after listening to well meaning but often misguided "back to nature" advocates. Unfortunately the consequences of activism based on a lack of understanding of biotechnology could seriously impair the advance of this most promising scientific venture. Scientists on the other hand have not always fully explored the potential risks of technological advances. But of course, there is no progress without some risk taking. Sure, it's conceivable that fifty years down the road some unexpected effect of BGH will crop up. But given that this hormone is the most thoroughly tested agricultural product ever, the prospect appears to be most unlikely. Whether the world really needs BGH, though, is another question. How will it affect milk prices? What will be its impact on small farms? Will fear of milk from treated cows cut down on dairy and consequently calcium consumption? Will the squabbling over labeling requirements further erode public confidence in our food supply? Will it play a role in alleviating nutritional problems in the developing world? Science cannot answer these questions, but as far as safety goes, the wealth of accumulated research has shown that recombinant bovine growth hormone is not the unexploded bomb some claim it to be. There might, however, be a little fire cracker hidden somewhere. And to be honest, we can get along without bovine growth hormone quite well.
