Facing a surge in drug-resistant infections, the World Health Organization issued a plea to farmers two years ago: "Stop using antibiotics in healthy animals." But at last year's big swine industry trade show, the World Pork Expo in Des Moines, one of the largest manufacturers of drugs for livestock was pushing the opposite message.

The company's Pig Zero brochures encouraged farmers to give antibiotics to every pig in their herds rather than waiting to treat a disease outbreak caused by an unknown Patient Zero. It was an appealing pitch for industrial farms, where crowded, germ-prone conditions have led to increasing reliance on drug interventions. The pamphlets also detailed how feeding pigs a daily regimen of two antibiotics would make them fatter and, as any farmer understands, a heavier pig is a more profitable pig.

The rise of drug-resistant germs, caused by overuse of antibiotics, is one of the world's most nettlesome health predicaments. Excessive use of the medicines has allowed germs to develop defenses against them, rendering a growing number of drugs ineffective for people and animals. The practices of livestock farmers, who for decades have used huge quantities of the drugs deemed important to humans, have long been viewed as one of the roots of the problem, but the role of the companies that make the drugs has received less scrutiny.

Antibiotics continue to be an important part of the business of companies like Elanco, which spun off from Eli Lilly in September, its share price soaring to $33 from $24. While Elanco is developing antibiotic alternatives for animals, like vaccines and enzymes, the antibiotics promoted by the Pig Zero campaign are exactly the kinds that global public health officials are trying to curb. And Elanco is no outlier - its rivals are also urging aggressive use of their own antibiotic cocktails.

"The reality is that antibiotics and large-scale industrial farming really grew up together," said Dr. Gail Hansen, a former state epidemiologist and state public health veterinarian in Kansas, who sits on advisory boards addressing antibiotic resistance. She equated the problem with climate change. "By the time people understand and believe it," Dr. Hansen said, "it may be too late."

Elanco had already been put on notice about the drugs used in its Pig Zero push. In 2015, the Food and Drug Administration warned Novartis Animal Health, which had been acquired by Elanco, that the same antibiotic cocktail was "unsafe" and "misbranded," because it was being illegally marketed to fatten pigs, rather than to simply treat disease. One of the drugs, tiamulin, has been a top seller for Elanco; the WHO views it as medically important to humans, but American regulators do not. Pig Zero trumpets the benefits of coupling tiamulin with chlortetracycline, a drug made by Elanco's competitors that both American and international regulators consider medically important to humans.

In an interview at Elanco's headquarters outside Indianapolis, Jeffrey Simmons, the chief executive, said the company had decided to change the program's marketing and to stop distributing the Pig Zero brochure after The New York Times began asking questions about it.

The connection of overuse of antibiotics in livestock to human health takes two paths: As bacteria develop defenses against drugs widely used in animals, those defense mechanisms can spread to other bacteria that infect humans; and, resistant germs are transmitted from livestock to humans - through undercooked meat, farm-animal feces seeping into waterways, waste lagoons that overflow after natural disasters, or when farm workers and others come into contact with animals.