Many health experts fear that the rise in antibiotic-resistant superbugs may be fuelled in large part by the rampant use of antibiotics among meat producers. Now, a new survey finds it's getting harder to find meat in your local grocery store that was grown without the drugs.

Consumer Reports' report finds that a number of the largest grocery chains in the U.S. don't offer any antibiotic-free meat. Among the 13 chains they surveyed, only Whole Foods guaranteed that all the meat and poultry sold in its stores was never treated with antibiotics.

Several others offered a selection of regular or antibiotic-free meat. But four big chains offered no antibiotic-free meat.

Antibiotics have been used in animal feed since the 1950s, to promote growth and to prevent disease spread among large farms where dozens, and sometimes thousands, of animals and birds are housed together in close quarters.

The amount of antibiotics typically given is considered "sub-therapeutic," meaning they're at low levels designed to prevent infection, not at the higher doses used to clear up infections. The Chicken Farmers of Canada's website says the medicines are added to prevent disease.

"Antibiotics help to maintain healthy birds, thereby ensuring a safe food supply for consumers," the group says.

But public health experts say their use in animal feed is likely contributing to antibiotic-resistant infections in humans.

It's not clear how many antibiotics are delivered to animals every year in Canada, but Consumer Reports says that in the U.S., the antibiotics given to poultry and livestock accounts for 80 per cent of all antibiotic use in the country. It says it's worried about the long-term effects.

"Antibiotics are losing their potency in people, leading to a major national health crisis, and we need to drastically reduce their use in food animal," says Jean Halloran, the director of Food Policy Initiatives for Consumers Union, which is the advocacy arm of Consumer Reports.

Earlier this year, World Health Organization Director-General Dr. Margaret Chan also expressed worry in an address to an international meeting on antibiotic resistance.

"Worldwide, the fact that greater quantities of antibiotics are used in healthy animals than in unhealthy humans is a cause for great concern," she said.

Consumer Reports recently conducted a poll of 1,000 Americans and found that 72 per cent said they were extremely or very concerned about the overuse of antibiotics in animal feed.

The poll also found that 86 per cent of respondents wanted meat raised without antibiotics to be sold in their local supermarket. And more than 60 per cent said they would be willing to pay at least five cents a pound more for meat raised without antibiotics.

But the group found it can be difficult to distinguish which meat and poultry comes from animals that have never been given antibiotics.

Labels such as "antibiotic-free," "no antibiotic residues," and "no antibiotic growth promotants" are not approved and can often be meaningless, they said. The term "natural" can also be confusing, since it does not ensure that antibiotics were not used, Consumer Reports says.

In Canada, the Canadian Food Inspection Agency says the term to look for is: "Raised without the use of antibiotics." In order for manufacturers to display that claim, the animal or fish in question must not have received any antibiotics, from birth to harvest.

The agency says the claim "Fed no antibiotics" is not helpful, since it may mean the animal may have received antibiotics through injection or spraying.