Monsanto, which is the sole producer of the growth hormone, has submitted a letter to the US Food and Drug Administration (FDA) and the Federal Trade Commission (FTC), calling for clear government labeling guidance and enforcement. It claims that firms labeling their products as rBST free are misleading consumers into thinking these products are superior to those from cows treated with the hormone, which received FDA approval in 1993. According to a dairy producer - one of the 500 "concerned individuals" who signed Monsanto's letters - "deceptive labels suggest to consumers that there is something wrong with the milk they have been drinking for the past 13 years. Even though the companies that print these labels know this is not true, they choose to mislead consumers in an effort to charge more money for the same milk." However, firms flagging up their milk as not containing the hormone say they want to provide consumers with the choice to make informed purchasing decisions. BST or bovine somatotropin is a naturally occurring protein hormone in the pituitary gland of cattle. However, Monsanto's synthetic version, rBST, is a growth hormone that is injected into a cow to increase milk production. The hormone, which Monsanto terms a "supplement", is widely used around the US. According to the firm's estimates, about one third of the nation's dairy cattle are given rBST. However, the practice is banned in Japan, Australia, New Zealand, Canada and most of the EU. Some scientific studies have indicated that rBST might be implicated in causing sterility, infertility, birth defects, cancer and immunological derangements in humans. In cows, it is thought to increase infections in cow udders, leading to more pus ending up in retail milk. Increasing consumer concerns have led to more and more dairy producers indicating that their milk does not come from cows treated with the hormone. Last year, Dean Foods, the largest processor and distributor of milk and dairy products in the country, also started to offer rBST-free milk products. But Monsanto has fiercely pursued the issue, resulting in numerous legal battles and some firms making changes to their labels. In 1994, FDA published voluntary guidance to the dairy industry, recommending a certain formula to adopt when making rBST-free claims. The agency said that because of the presence of natural bST in milk, no milk is 'bST-free,' and a 'bST-free' labeling statement would be false. It added that it was also "concerned" that the term 'rbST free' may imply a compositional difference between milk from treated and untreated cows rather than a difference in the way the milk is produced. FDA said that misleading implications could best be avoided by the use of accompanying information that puts the statement in a proper context. For example, accompanying the statement "from cows not treated with rbST'' with the statement that "No significant difference has been shown between milk derived from rbST-treated and non-rbST-treated cows''. In 2003, FDA sent warning letters to a number of manufacturers of whole milk, reduced fat milk and ice cream, which had been labeled as 'hormone free'. These claims, said the agency, were false because of the naturally occurring hormones in milk, and the manufacturers were requested to change their labeling. Firms highlighted by Monsanto's latest letters to the regulators include Stonyfield Farm, Thomas Dairy, Kleinpeter Dairy and Wilcox Family Farms. To view Monsanto's letters, as well as attachments including examples of the labeling it disputes, click here. To view FDA's guidance on the voluntary labeling of dairy products from cows not treated with sBST, click here.