It's not hard to understand when you examine our broken federal food safety system. The latest case example: 143 million pounds of beef were recalled this month by the federal government in the largest beef recall in U.S. history.

What happened?

Those pesky activists at the Humane Society of the United States went undercover at California-based Westland/Hallmark Meat Co. to document extreme violations of federal regulations governing the humane treatment of animals killed for their meat. Despite the presence of a full-time, on-site inspector from the U.S. Department of Agriculture, downer cows -- those cows too sick or injured to stand up on their own -- were tortured and forced to stand up long enough to be killed.

What's wrong with that, aside from the obvious ethical questions?

Downer cows are considered to have a higher probability of carrying the prions that cause brain-wasting bovine spongiform encephalopathy, or mad cow disease. A form of the incurable disease, variant Creutzfeldt-Jakob disease, or vCJD, is thought to be passed to humans who eat infected meat. Prions can't be destroyed by heat from cooking.

Much of the recalled meat was distributed to 36 states for use in the National School Lunch Program. Twenty-five North Carolina school systems, including Wake, Chapel Hill-Carrboro and Charlotte-Mecklenburg, had received 126,000 pounds of the recalled meat. Of that amount, 104,000 pounds were still in storage at the time of the recall, according to the N.C. Department of Agriculture.

The USDA's assurances that its food protection "interlocking safeguards" are working fall flat, given abundant evidence to the contrary. So do government officials' observations that nobody got sick after eating the meat from the downer cows. Scientists believe it can take years, or even decades, after exposure to prions before vCJD develops.

What now?

First, we need an independent agency put in charge of protecting the food supply. The USDA has demonstrated yet again it can no longer be trusted with the job.

That's because when USDA is supposed to be ensuring the safety of our food, it is also charged with promoting the interests of agriculture.

The final link in this broken chain: The USDA also runs the nation's nutrition programs, including the National School Lunch Program.

From the feedlot to the lunch tray, it's a system designed more to serve the interests of an industry than the interests of the public.

One lawmaker, Rep. Rosa L. DeLauro, a Democrat from Connecticut who chairs the House Agriculture, Food and Drug Administration Appropriations Subcommittee, has called for an investigation into the USDA's ability to properly ensure the safety of food served in schools.

But don't expect any real change any time soon. The public isn't clamoring for a fix.

Michael Swanson, an agricultural economist, pinned the problem in an interview with Reuters: "It has to be in the first five minutes of a newscast and they have to have a picture of somebody suffering for it to register. Until that happens, it is a nonevent."

The risk is there, however. And until we set up an independent, federal food safety and inspection service, we can all look forward to the next record-breaking beef recall.