Wal-Mart Stores called Friday for meat suppliers to their US operations to curb the use of antibiotics and follow globally recognized guidelines on humane treatment of farm animals.
The push was directed at suppliers to Walmart US and Sam's Club, which counted on groceries for more than half of their annual revenues last year of $346 billion.
"Our customers want to know more about how their food is grown and raised, and where it comes from," said Kathleen McLaughlin, senior vice president of Walmart sustainability.
"As the nation's largest grocer, Walmart is committed to using our strengths to drive transparency and improvement across the supply chain."
Key steps include asking suppliers to use antibiotics for treating ill livestock but not to promote growth, the world's largest retailer said.
The Bentonville, Arkansas-based company also wants the suppliers to provide an annual public report on antibiotic use.
The announcement comes amid a major global push to reduce inappropriate antibiotic use, blamed for increasing the proliferation of drug-resistant bacteria, or "superbugs", that turn long-treatable diseases into killers.
President Barack Obama rolled out measures in March aimed at fighting doctors' overprescription of antibiotics, aiming to slash their use by 50 percent for outpatients and 20 percent for inpatients.
According to the Centers for Disease Control and Prevention, drug-resistant bacteria kill 23,000 people a year in the United States.
Walmart's move came as an increasing number of supermarkets and fast-food chains join the campaign to limit the use of antibiotics on farm animals, especially antibiotics used also for humans.
In the past year Chik-Fil-A and McDonald's, among others, have moved to eliminate chickens fed with human antibiotics from their menus.
Under pressure, Tyson Foods, the largest US poultry producer, announced in late April that it would eliminate human antibiotics from its broiler chickens in US farms by late 2017.
A major Tyson competitor, Perdue Farms, which has not used antibiotics to promote growth in its chicken production since 2007, said in September it had removed all antibiotics from its hatcheries.
Walmart also said Friday that it backed the globally recognized "Five Freedoms" of animal welfare that includes protections from pain, injury or disease and freedom from discomfort through adequate housing.
Humane Society president Wayne Pacelle praised the retailer's moves, saying they signal "an extraordinary change in agriculture in America.
"Precisely because it's Walmart, this is the most definitive statement yet that the era of confining farm animals in cages will come to an end," he said.
Pacelle said the actions would help to end what he said were inhumane conditions for hens, sows and calves, and would lead to more humane forms of slaughter.
He said the announcement was a "first step" and that Walmart still needed to produce timetables for implementing many of the commitments.
"But this will be a day long remembered," Pacelle said.