Based on what? The Japaneses test every cow/steer.. I haven't heard it has stopped their demand for beef.
Based upon the tinfoil theory that the government has a reason to not want the testing done - they are afraid that the results will show that the mad cow prions are more widespread than people have been told.
If there is nothing to hide, why are they trying so hard to hide it.
Given what they pay for beef, the added cost is probably negligible.