In California when selling and animal you are required to sign a tag that reads:
I hereby certify, under penalty of perjury, that the information provided is true and correct, and that all eligible female cattle are Brucellosis vaccinated and bear evidence of such vaccination as required by California Agricultural Code..... etc.
Not sure if this is the only state that requires this tag or not. I will say however that having worked for an auction yard we NEVER checked for bangs identification just that they signed the paper.
We did hear however that the buffalo heards in yosimity (sp?) national park are thought to be carying brucellosis. Not sure if that was a sure thing or not. You know how the media is.......
Double R