OK, a genuine question then, mocnarf - In the UK, all breeding sheep must be given two ear tags which uniquely identify them. One of these is a standard tag, and the other has an RFID chip in it that can be read electronically as the sheep passes through markets, slaughterhouses etc.
When we move sheep from one place to another, or if they are sold, we also have to fill in a form with each of the sheep's identification numbers on it, which has to be sent in to the government so they can keep a track of animal movements etc. (That's why TimW made the comment about sheep walking requiring rather a lot of paperwork!).
I'm intrigued then - do you have any compulsory ID tagging or movement registration for farm animals in the USA?