BY JACK DINI – Do you prefer eggs from free-range hens over those from caged hens? If so, here’s some upsetting news.

A recent Taiwanese study found that free-range chickens in Taiwan have an average of 5.7 times higher levels of dioxin than their counterpart caged hens.

According to the researchers, this occurs because free-range chickens spend the majority of their lives outside, and are therefore exposed to more environmental contaminants than caged chickens, which are kept indoors. (1)

First, a review of the definition of free-range. According to Wikipedia, “Free-range is a term which outside of the United States denotes a method of farming husbandry where the animals are allowed to roam freely instead of being contained in any manner. In the US, USDA regulations apply only to poultry and indicate that the animal has been allowed access to the outside. The USDA regulations do not specify the quality or size of the outside range nor the duration of time an animal must have access to the outside. Free-range may apply to meat, eggs or dairy farming.” (2)

“You may picture a cow grazing on a lush hillside while chickens peck away at the ground, but get this: The term free-range is absolutely unregulated for eggs, beef or any food except live poultry. It’s a marketing claim with no standard definition and no government agency enforcing it. The only way to know what free-range means is by asking the farmer or calling the company that produced the food,” reports Sally Deneen. (3) Of note is the fact that California recently passed a law requiring that by 2015 hens should be able to freely lie down, stand up, and extend their wings. The law essentially bans the use of small cages that cram the animals so tightly they sometimes cannot turn around. An extension of the law, signed by the governor, means that farms outside California will have to abide by California’s human treatment law if they want to sell eggs there. (4)

Rod Dreher notes, “Free-range as a label means very little. Chicken can quality as free-range even if it’s packed into a 100-yard shed with no maneuverability. A free-range pig can be raised as a conventional pig for nine months, purchased by a free-range farm, pastured for three months and sold as free-range. The consumer is led to think it was always free-range. More alarmingly, a wealth of evidence suggests that free-range pigs come into frequent contact with harmful pathogens and worms.”  Dreher adds, “The factory farm is, quite frankly, an environmental nightmare. Its problems are well known. We should not support it. But the commonly proposed alternative—the free-range option—comes with significant problems that the media, which is overly enamored with these operations, tend to ignore.” (5)

One downside is that free-range animals can produce more contaminants. Besides the dioxin issue mentioned earlier, Karen Kaplan reports, “The problem probably isn’t limited to Taiwan. Scientists have found the same trend in the European Union, and one study found that about 10 percent of free-range eggs exceeded the safety limit set by regulators there.” (6) Diseases spread more rapidly than in caged farms because free-range birds must trample through their own excrement rather than live in cages mercifully suspended above the floor of poop. (7)

Texas State University professor James McWilliams wonders why the food media is ignoring studies pointing to pastured meat animals as carriers of communicable diseases. He says recent studies point to higher concentrations of parasitic diseases like Trichinella and Toxoplasma in free-range pigs versus their caged cousins. He adds, “Pastured chickens are much more likely to contain Salmonella. Some 30-50 percent of free-range birds and as many as 100 percent of backyard birds are little strutting Salmonella factories. In the same studies, caged chickens had an infection rate under 3 percent.” (7)

Pigs have more maneuverability, meaning that free-range pigs enjoy access to genuine outdoor space. No stalls or crates are permitted on free-range farms. However, a recent report highlights the dangers of assuming that free-range pork is the answer to conventional feedlot pork. The study found that naturally raised antibiotic-free pigs contained higher rates than conventionally raised pigs of the antibodies for three common and dangerous foodborne pathogens. Free-range pigs had almost five times as much Toxoplasma Gondii, more than half had Salmonella (compared with 39 percent of conventional pigs), and perhaps most distressing, 2 of the 616 studies tested for Trichinella spiralis, a parasite that agricultural scientists thought had been completely eliminated from the pork supply. (8)

In discussing this study, McWilliams observes, “One irony is hard to escape: when farm animals are returned to ‘natural’ conditions, they encounter the very same wilderness-related problems that led farmers to corral them into feedlots in the first place, Indeed, the authors of the report believe that the free-range pigs contracted higher rates of parasites as a result of their interaction with wild animals and, oddly enough, domestic cats, which can carry these parasites.” (7)

Another issue has to do with greenhouse emissions. Livestock are a leading source of greenhouse gases. The raising and processing of cattle, hogs, poultry and other animals produces 18 percent of greenhouse gases; by comparison 13 percent comes from trucks, cars and other transportation. In addition, the livestock sector generates 65 percent of human-related nitrous oxide, which has almost 300 times the Global Warming Potential (GWP) of carbon dioxide. (9)

Confinement feeding of livestock helps sharply reduce greenhouse emissions, according to a recent Stanford University report. Dennis Avery estimates that it would take the land area of New Jersey for chicken ‘playgrounds’ if we put all our birds outdoors. It would take the land area of Pennsylvania to raise our hogs on free ranges. (10)

Feedlot cattle eating grain from high-yield fields produce less methane in their guts than cattle digesting grass because grass is harder to digest. Studies on beef cattle show methane emissions reduced by 38 to 70 percent. Confinement feeding also protects our streams and rivers. The manure from outdoor animals washes into the nearest creek. The wastes from confinement animals are collected and used as organic fertilizer on crops. (10)

So what’s a person to do? The idea of a free-range animal makes us feel better about eating. It soothes our minds somewhat about the animal. It also means the animals are not receiving the antibiotics and vaccines that keep them growing in caged systems. Yet, as recent information suggests, there is a downside. Free-range has its share of problems. This isn’t to say that free-range animals represent some health food crisis. However, we should be aware that free-range has escaped some of the scrutiny we’ve applied to caged animals.


  1. Jing-Fang Hsut, Chun Chen and Pao-Chi Liao, “Elevated PCDD/F Levels and Distinctive PCDD/F Congener Profiles in Free-Range Eggs,” J. Agric. Food Chem. DOI:10.1021/jf100456b, June 3, 2010
  2. “Free Range”, Wikipedia, accessed June 24, 2010
  3. Sally Deneen, “Free-Range Foods,”, accessed June 24, 2010
  4. Wyatt Buchanan, “Egg mandate now applies to imports,” San Francisco Chronicle, July 7, 2010, Page C1
  5. Rod Dreher, “James McWilliams, the contrarian agrarian on our food future,” Dallas News, April 24, 2009
  6. Karen Kaplan, “Free-Range Eggs Contain a Little Something Extra: Pollutants,” Los Angeles Times, June 16, 2010
  7. James E. McWilliams, Just Food, (New York, Little, Brown and Company, 2009), 148-152
  8. Wondwossen A. Gebreyes, et al., “Seroprevalence of Trichinella, Toxoplasma, and Salmonella in Antimicrobial-Free and Conventional Swine Production Systems,” Foodborne Pathogens and Disease, 5, 199, 2008
  9. Henning Steinfeld, et al., “Livestock’s Long Shadow,” Food and Agriculture Organization of the United Nations, Rome 2006
  10. Dennis T. Avery, “Confined livestock better for the planet,”, July 6, 2010

Jack Dini was a materials engineer and Section Leader at Lawrence Livermore National Laboratory. He is the author of two books, Electrodeposition-The Materials Science of Coatings and Substrates (1993), and Challenging Environmental Mythology (2003). Since 1998 he has been writing a monthly column titled “Fact or Fiction?” for Plating and Surface Finishing (P&SF). He has also written for a number of other publications.