In addition, and more salient to the regulation of composition claims like “rbST free,” the failure to discover rbST in conventional milk is not necessarily because the artificial hormone is absent in such milk, but rather because scientists have been unable to perfect a
test to detect it. As recognized by the State's brief in the district court, “given existing technology, it is currently impossible to test milk to determine whether the hormones present are natural hormones or recombinant hormones (such as rbST).” The State further conceded this point at oral argument, acknowledging that conventional milk “could” contain rbST, but that no test has been able to verify if this is in fact the case. This uncertainty is also implicit in the FDA's 1994 Guidance. There, the agency stated that “there [i]s no
significant difference between milk from treated and untreated cows” because “[t]here is currently no way to differentiate analytically between naturally occurring bST and [r]bST in
milk.” 59 Fed.Reg. 6279, 6280 (emphasis added). The FDA thus appears to have left room for the fact that
some compositional difference between the two types of milk may exist, leaving open the possibility that one day a method might exist to detect whether rbST is in fact present in conventional milk.