In recent years, however, newly perfected genetic engineering techniques have enabled scientists to produce the hormone in sufficient quantity and quality for intensive study. The sponsor must also provide adequate data on the environmental impact of the drug's use. However, in the meantime, FDA has allowed the marketing of meat and milk from bST-supplemented cows in experimental herds because it has determined that these foods meet the requirement of federal law. Federal law permits the commercial sale of food products from animals in investigational studies only when the sponsor has demonstrated that they present no public health risk. That is why cows must be injected with bST for it to be effective.
Rats are an appropriate model because bST is biologically active in rats when injected.
Thus, any bST escaping digestion in the rat would have biological effects, such as effects on growth. Studies indicate that bST is not effective in humans and other primates even if injected. BST is a natural constituent of milk. It is produced by the pituitary gland and has always been present in the meat and milk of cows. The bST injected to increase milk production merely increases the amount to which the cow is exposed.