Bovine somatotrophin (BST)

In cows, milk production is influenced by the complex interaction of a range of hormones. Bovine somatotrophin (BST) is a natural growth hormone that occurs in cattle and controls the amount of milk that they produce. In 1994 Monsanto began marketing a synthetic version of BST, known as recombinant BST (rBST), which was sold as Posilac. Injecting dairy cows with rBST alters the metabolism to increase milk production by up to 15 per cent. Since its introduction in 1994, Posilac has become the largest selling dairy animal pharmaceutical product in the US. Sold in all 50 states, rBST is used in around one-third of the nine million dairy cows in the US (Monsanto, 2005).

While the US Food and Drug Administration (FDA) permit the use of rBST, its use is associated with severe welfare problems, for example increasing the incidence of lameness and mastitis. For reasons of animal health and welfare, the use of rBST in the EU was prohibited in 2000. Indeed Canada, Japan and many other countries have banned the use of rBST because of its effects on animal health and welfare. However, there are no restrictions on the import of rBST dairy products, or any requirement to label them.
The Government’s Veterinary Medicines Directorate does not carry out any testing of imported milk (Defra, 2006). Furthermore, Defra confirmed in correspondence with the VVF, that since the EU is a single market once a product has entered, if it is transported on to another country within the EU, then the origin of the product will be the EU country rather than the originating country (Defra, 2006). In 2005, the UK imported over 1,000 tons of dairy products (mainly ice-cream) from the US (Defra, 2006a); these figures have declined from over 5,000 tons in both 2001 and 2002 but still remain a concern, especially as the consumer has a limited chance of discriminating against imports from the US. The sensible option is to avoid all dairy products.

Concern has been expressed over several health issues associated with the use of rBST. The increased incidence of lameness and mastitis in rBST-treated cows inevitably leads to an increased use of antibiotics to treat these and other infections. Over half of the antibiotics that are produced in the US are used for agricultural purposes (Mellon et al., 2001). Antibiotic use is known to promote the development of antibiotic resistance. Thus the widespread use of these drugs has contributed to the high frequency of resistant bacteria in the intestinal flora of farmed animals (Lipsitch et al., 2002). This raises concerns about the development of antibiotic resistant infections in humans. A study in the New England Journal of Medicine in 2000 reported that the emergence of antibiotic-resistant strains of Salmonella is associated with the use of antibiotics in cattle. This study described how a new antibiotic-resistant strain of Salmonella was isolated from a 12-year-old boy admitted to hospital with abdominal pain, vomiting and diarrhoea. The boy lived on a ranch in Nebraska and subsequent investigation revealed the presence of the identical strain of bacteria, resistant to the antibiotic ceftriaxone, among cattle on his family’s ranch and nearby ranches that had suffered outbreaks of salmonellosis. The cattle had been treated with ceftriaxone. This evidence suggests that the boy’s gastrointestinal infection was acquired from cattle (Fey et al., 2000). The obvious concern here is that the widespread use of antibiotics in cattle can lead to an increase in antibiotic-resistant strains that may subsequently transmit to humans. This is a public health concern and the question must be asked: how much evidence of harm do we need before we much further restrict the use of antibiotics in farm animals?

Milk production increases in cows treated with rBST because it promotes the production of the naturally occurring growth hormone insulin-like growth factor 1 (IGF-1) which then stimulates the glands in the cow’s udders to produce more milk. Research shows that rBST use on dairy cows can substantially increase the levels of IGF-1 in their milk (Prosser et al., 1989). This raises concerns about the potential biological action of IGF-1 from cow’s milk in humans especially because IGF-1 from cows is identical to human IGF-1. Professor Samuel Epstein, an international leading authority on the causes and prevention of cancer, warns that converging lines of evidence incriminate IGF-1 in rBST milk as a potential risk factor for both breast and gastrointestinal cancers (Epstein, 1996).

So why should this concern us if we do not allow the use of rBST in the UK? Well in terms of human health, the concern is that milk and milk products imported from countries that permit the use of rBST may lead to the consumption of foods that promote increased levels of IGF-1 in humans. In 1999, the minister of state, Baroness Hayman, referred to a report from the Veterinary Products Committee (VPC) which stated that while the use of rBST does not increase the level of BST found naturally in cow’s milk, there is a two-to-five fold increase the level of IGF-1 in the milk, which she acknowledged may be implicated in the occurrence of colonic cancer. However, Hayman reiterated the VPC’s view that the risk to human health was likely to be extremely small. Hayman also suggested that just 0.3 per cent of total milk and milk products imported into the UK come from the US where rBST is authorised for use (UK Parliament, 1999). (See IGF-1).