In its investigation, The Star examined the largest beef packers, including the big four — Tyson Foods of Arkansas, Cargill Meat Solutions of Wichita, Kan., National Beef of Kansas City, Mo., and JBS of Brazil — as well as the intertwined network of feedlots, processing plants, animal drug companies and lobbyists who make up the behemoth known as Big Beef.

Today’s ever-larger feedlots use an intensive antibiotic regimen, even though the USDA reports that such practices contribute to antibiotic-resistant bacteria in humans.

But Big Beef maintains that concerns about antibiotic overuse in livestock are overblown. The Animal Health Institute, the lobbying arm of the animal pharmaceutical industry, said there’s not enough data to compare antibiotic use in animals and humans, citing a Food and Drug Administration statement that said it is “difficult to draw definite conclusions.”

The industry said antibiotics are needed for the humane treatment of sick and suffering animals and added that there is no “provable connection” between the cases in Joplin and livestock antibiotic use.

Before cattle are slaughtered, they’ve been fed, tagged and injected with millions of dollars of hormones, growth promoters and antibiotics.

Every year, about 29 million pounds of antimicrobial drugs are used on cattle, pigs and poultry, government data show.

But the government doesn’t make public how much of those drugs are used in cattle, or any other meat animals, because it considers that information a “trade secret” and its release might give one meat producer a competitive advantage over another.

A public interest group, however, sued the FDA to force the release of additional data on antibiotics used in food animals.

“How can we truly know the extent to which these drugs are causing harm if we can’t even access the information?” said Amanda Hitt, director of the food integrity campaign at the Government Accountability Project, a whistle-blower protection group.

GAP sued when FDA refused to release the data under a Freedom of Information Act request.

The Animal Health Institute said that data it collected until 2007 showed that about one-third of the compounds used in food animals are not used in humans and therefore “cannot in any way contribute to the burden of antibiotic resistance in humans.”

Which means two-thirds of those used in food animals are used in humans. So why does Big Beef keep using them?

Cattlemen have known for decades that antibiotics cause digestive changes in cattle that help them efficiently convert corn into added weight.

And that saves money.

Before the 1950s, most cattle primarily ate grass until they were slaughtered. But after World War II, farmers learned they could feed large numbers of cattle on less acreage by using more corn instead of grass.

However, there were unintended consequences.

Animals in confined spaces spread diseases. Cattle on high rations of corn develop acid buildup, which can deteriorate the gut lining — similar to an ulcer in humans — and cause gas, bloating and lameness.

Corn can eat away part of a cow’s stomach, said Allen Williams, a former feedlot owner and cattle specialist at Mississippi State University.

Big Beef soon discovered antibiotics controlled both problems.