the republican from florida has been mentioned as a possible running mate for mitt romney. no word on the nature of the threat, but police are taking precautions. one day after we learned that a dairy cow in california had mad cow disease, the u.s. department of agriculture is moving to see if it is an isolated case. we asked wyatt andrews to look into what's being done and find out how much we know about the health of cattle. >> reporter: investigators are combing through dairy farm records in tulare county, california, trying to identify where the sick cow was born and if she ever gave birth. despite assurances the cow had atypical or naturally occurring mad cow disease, the u.s.d.a. still operates as if the cow was contagious. under international guidelines, every cow born in the same herd and every calf born to the sick cow must be found and destroyed. dr. john clifford is the chief veterinarian at u.s.d.a.