In April the FDA-CVM denied a citizen's petition requesting that the agency rescind its approval of a recombinant bovine somatotropin (rBST) product used to increase milk production in dairy cattle up to 15 percent.
Robert Cohen, executive director of the Anti-Dairy Coalition, had petitioned the FDA to ban Posilac, a Monsanto Company product, and remove it from the market on the basis of "new evidence" that the product poses "serious health consequences for human consumers."
Since its approval in 1993, Posilac has come under fire in the United States and abroad for its alleged harmful effects to humans and animals. More than a year ago the Canadian government declared that the hormone increases the likelihood of health problems in dairy cattle, and would be prohibited in the country (see JAVMA, April 1, 1999, page 985). The hormone is also banned in the European Union for animal welfare reasons.
At about the same time of the Canadian decision, concern over the hormone from both US senators in Vermont evoked a response from Health and Human Services Secretary Donna Shalala. After an extensive review of the human food safety actions of the Investigational New Animal Drug file and master file, the FDA stood by its endorsement of Posilac's safety and efficacy, Shalala told the senators.
Cohen had stated in his petition that, contrary to the agency's conclusions, humans drinking milk from cattle treated with rBST absorb unsafe concentrations of insulin-like growth factor-1 (IGF-I), as well as the hormone itself.
Additionally, he insisted that Monsanto changed its manufacturing process for rBST after the studies supporting the New Animal Drug Application were completed, thereby invalidating the research used to support Posilac's approval.
In its reply, the FDA said it believed that the arguments do not demonstrate any human food safety issue related to the use of Posilac. The petition requesting withdrawal of the approval was, therefore, denied.
The FDA stated that concentrations of IGF-I in milk are not significant when evaluated against concentrations of IGF-I endogenously produced and present in humans. IGF-I is a normal but highly variable constituent of bovine milk, with the concentration depending on the animal's stage of lactation, nutritional status, and age. Although some studies indicate that concentrations of IGF-I may statistically increase in the milk of rBST-treated cows compared with untreated cows, reported increases are still within the normal variation of IGF-I concentrations in milk.
Like most dietary proteins, rBST is degraded by digestive enzymes in the gastrointestinal tract and is not absorbed intact, the agency said.
Finally, the FDA was fully aware of the change in Monsanto's manufacturing process prior to approval. To reaffirm the conclusion of Posilac's safety, however, the agency reexamined information previously submitted by the company to support approval of the rBST.
For another perspective on this controversial issue, see the "Forum" feature in the June 1, 2000 JAVMA, page 1719.