Given that people are worried about the disease, one might expect that private beef companies would step in and start voluntarily testing their cattle before selling it (labeling the resulting beef as "mad-cow free" or some such). You've probably noticed that no such products are on the market.
Why? The USDA has threatened to sue any company that tests for mad cow separately from the government program (most notably Creekstone Farms). Just a few days ago this ridiculous prohibition was stopped by a federal judge, and, assuming that the government doesn't appeal the decision, private companies will now be free to test their own cattle for the disease.
Here's an excerpt from the New York Times article that has a bit more background on the specific case:
Creekstone Farms Premium Beef, a meatpacker based in Arkansas City, Kan., wants to test all of its cows for [mad cow] disease, which can be fatal to humans who eat tainted beef. Larger meat companies feared that move because if Creekstone tested its meat and advertised it as safe, they could be forced to do the expensive test, too.
The Agriculture Department currently regulates the test and administers it to less than 1 percent of slaughtered cows. The department threatened Creekstone with prosecution if it tested all its animals.
U.S. District Judge James Robertson ruled that the government does not have the authority to regulate the test. Robertson put his order on hold until the government can appeal. If the government does not appeal by June 1, he said the ruling would take effect....
The Agriculture Department argued that widespread testing could lead to a false positive that would harm the meat industry. Robertson said he was concerned by that possibility but noted that Creekstone sought to use the same test the government relies on.