NEW YORK (NYTimes) - Shoppers buying a dozen eggs these days not only have to decide whether they want organic, free-range or cage-free. They also have to choose among cartons with labels like "American Humane Certified," "Animal Welfare Approved" and "Certified Humane."

As the number of consumers concerned about animal welfare grows, such labels, or seals, as they are known in the business, are spreading like kudzu on packages of meat and eggs in the refrigerated cases of grocery stores, to assure shoppers that the cattle, pigs or chickens were treated well.

But the labels may just as easily sow confusion or even mislead shoppers, who probably know little or nothing about the small number of organisations that create most of them and police the food producers that use them.

"Consumers are looking behind the barn doors at these factory farms, and they don't like what they're seeing," said Daisy Freund, the director of farm animal welfare at the American Society for the Prevention of Cruelty to Animals, which created a website last year to help consumers navigate the seals. "Unfortunately, we know that when they hit the grocery store, they're faced with a profound lack of transparency, accountability and, in some cases, downright deception when it comes to statements on packaging about humane treatment of animals." So what are shoppers to make of these labels?

Most are issued by three non-profit groups - the American Humane Association, Humane Farm Animal Care and A Greener World - that set their own standards for the practices needed to win certification. Food companies pay fees to use the labels; more than 1 billion of the more than 9 billion animals raised for food each year in the United States are covered by a certification program.

In addition, Whole Foods established the Global Animal Partnership, a five-step certification program it requires its suppliers to use; it is also used by a few small meat companies and small retailers.

Federal organic regulations set standards for animal care, though in some cases they are less rigorous than those of private certification groups.

But the phrases on the labels have no set meaning; the federal government has no rules for the use of words like "humane." The term "free-range" on a product, for example, does not necessarily mean that an animal had access to pasture.

The Agriculture Department does offer guidelines to meat producers, and requires them to submit applications and get permission before using terms like "humanely raised" or "raised with care" on packages. But it does not send out inspectors to test those claims.

"It's just a paperwork review," said Dena Jones, the director of the farm animal program of the Animal Welfare Institute. "A producer has to fill out a very simple form, one page, two sides, and submit some supporting information." That may be a one-sentence affidavit declaring something like, "I take good care of my animals," she said. In some cases, meat companies submit their certifications from the labelling organisations; Jones' group would like the federal government to require that all companies do the same.

Even that is not an ideal solution.

"Not all certification seals are created equal," said Andrew DeCoriolis, a program director at Farm Forward, an animal advocacy group. "Companies can essentially pick the standards that are the easiest for them to meet." DeCoriolis and many other animal welfare advocates say it is no wonder the largest of the certifying groups is the American Humane Association, the group behind the "American Humane Certified" seal. Many of its standards, the advocates say, are less rigorous than other groups', and therefore preferred by meat companies.

The advocates noted that a number of the group's standards are similar to those used in the meat industry. For instance, American Humane allows the level of ammonia in chicken houses to reach 25 parts per million - the standard the chicken industry recommends, and higher than the maximum level set by some other certifiers. High levels can render the birds sluggish and less likely to move, and even kill them.

The group also allows farmers to wean piglets at 21 days, an industry standard that is a week less than what is permitted by two other certifiers, and half the time a piglet must suckle under standards set by Animal Welfare Approved, the certification program of A Greener World, which works to change agricultural practices.

While other certifying groups require complete compliance with their standards, American Humane requires only that its clients achieve 85 per cent of the total points possible for award during an audit (although they are asked to comply fully at some point).

In May, American Humane stirred concern among other animal welfare groups by hiring as its director of marketing a lobbyist from Berman and Co., a public relations firm that is waging a forceful campaign against the Humane Society of the United States and People for the Ethical Treatment of Animals.

Robin Ganzert, the chief executive of American Humane, did not respond to emails or texts requesting an interview.

Not all of American Humane's standards are lower. For instance, it requires at least 21-3/4 sq-ft of outdoor space for hens laying eggs to be labeled free-range, or roughly 10 times the amount of space such hens must have to win the "Certified Humane" seal from the animal welfare certification program of Humane Farm Animal Care. (Humane Farm Animal Care defends its minimum of 2 sq-ft, saying it ensures that "hens will not have to go far to find cover, shade and nutrients.")

That difference led the Happy Egg Co., a free-range egg operation owned by the British firm Noble Foods, to switch from Humane Farm Animal Care to American Humane in 2015.

"Two square feet per bird is not appropriate," said David Wagstaff, the president of Happy Egg. "It's fundamentally flawed from a standards perspective."

Such nuances make parsing the various labels difficult for shoppers.

"I don't think many consumers understand that there are these differences in certification standards," said Temple Grandin, an animal scientist and noted champion of animal welfare.

Grandin is on American Humane's scientific advisory board and advises other certification groups. She acknowledged that the organisation's standards are not as rigorous as others', but said it played to a special segment of the meat industry.

"What AHA is trying to do is work with large-scale commercial producers so that they have at least some standards," she said. "But if you're looking for strict confirmation of how long a cow has been in a feedlot, AHA probably isn't going to pass muster." Consumers Union, the publisher of Consumer Reports, has been reassessing its evaluation of the standards set by the groups.

"The only one we have any confidence in and think gives you value for your money is Animal Welfare Approved," said Jean Halloran, director of food policy initiatives at Consumers Union. "The rest of them have, to greater and lesser degrees, shortcomings - and American Humane in particular has a lot of shortcomings."