The Green Lantern

Pork, chicken, milk and eggs have similar environmental impact

(Michael Sloan For The Washington Post)
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By Nina Shen Rastogi
Tuesday, June 1, 2010

Lantern, you've covered the environmental impact of meat a number of times. Where do eggs fit in? And would it be better for the planet to buy free-range or cage-free eggs?

The Lantern has good news for those of you who, like her, are devotees of the 24-hour breakfast menu: According to the best data we have so far, eggs are on the green end of the animal-protein spectrum. That doesn't mean they're particularly good for the planet, however. An omelet may have less of an impact than a strip steak or a pulled-pork platter, but eggs aren't necessarily any greener than the chickens that lay them.

In a report published in Livestock Science this spring, two Dutch researchers gathered data from 16 life-cycle analyses to compare the environmental impacts of five conventionally raised animal products: pork, chicken, beef, milk and eggs. On a per-kilogram-of-protein basis, nearly all the data showed that beef production requires the most land and energy and produces the most greenhouse gas -- often by a significant amount. When it comes to ranking pork, chicken, milk and eggs, the differences weren't that clear.

Take land use. Producing one kilogram of chicken protein (roughly the amount found in three dozen chicken breasts) requires 42 to 52 square meters of land. To get a kilogram of egg protein (what you'd get from about 10 dozen eggs), you need roughly the same amount: 35 to 48 meters. Pork came in a bit higher, at 47 to 64 square meters, and milk a little lower, at 33 to 59. But there's enough overlap among the reported ranges that you can't always make a clear call one way or the other. The reported ranges for energy use also overlapped, with pork having the highest numbers and milk the lowest, and chicken and eggs somewhere in the middle.

What about different types of eggs? Could you make a greener omelet by choosing cage-free or organic eggs over the conventional type?

Since the majority of the impacts associated with chicken-rearing comes from producing their feed, one way to look at the question is as a matter of efficiency: Which type of bird does the best job turning the food it eats into the eggs we eat? In that sense, there's a pretty clear hierarchy, according to Hongwei Xin, director of the Egg Industry Center at Iowa State University.

Data from Europe indicate that chickens raised in conventional cage systems -- the much-maligned rows of small "battery" cages -- are the most efficient layers: It takes them about two kilograms of feed to produce one kilogram of eggs. Chickens raised in cage-free or barn systems -- in which the birds roam freely around the building but don't necessarily have access to the outdoors -- require about 14 percent more food. Free-range birds, which have access to the outdoors, require about 18 percent more feed than conventional caged birds. Organic chickens, whose feed is grown without chemical fertilizers or pesticides, need roughly 20 percent more food than birds kept in cages.

The differences in feed efficiency arise in part because cage systems allow farmers to calibrate the birds' temperature, so the animals expend less energy keeping themselves warm. That energy can then go toward making more eggs. Chickens in non-cage systems also waddle around and flap their wings a lot more than their cooped-up cousins, which leaves even less energy for laying eggs. Plus, mortality rates are often higher when birds are allowed to roam. Finally, in non-cage systems, it's harder to regulate the ammonia emissions from chicken poop -- a major issue of environmental concern on poultry farms.

Of course, many green-minded consumers prefer eggs from uncaged hens precisely because of things that reduce their efficiency as egg layers: the freedom to exercise and engage in natural behaviors such as nesting and dust-bathing. (Keep in mind that "free-range" doesn't always mean that the hen spent its days frolicking in sun-kissed fields; it could mean the bird had some access to a concrete lot.) In addition, organic eggs may come with benefits that aren't necessarily reflected when you judge by efficiency alone -- benefits such as a reduction in pesticide and fertilizer applications, which is good for soil and water quality.

What if you decide to skip the supermarket and get your frittata fixings from the farmers market or another local purveyor?

Well, besides the happy, satisfied glow that comes from knowing where your food is produced, buying from a well-managed small farm can have eco-benefits. On a farm that rotates cattle and chickens on the same pastureland, for example, hens can pick out and eat the bugs from cowpies, providing the bird with important nutrients and helping tamp down fly problems. Birds that are "pasture raised" -- i.e., that eat a lot of insects and grass alongside regular feed -- may also have health benefits, including producing eggs with higher levels of omega-3 fatty acids.

Whether small-scale farms can meet the world's egg demands is another question -- and a crucial one to consider in terms of the overall sustainability of our food systems. But for her personal grocery needs, the Lantern likes going small and local when she can.

Finally, what if you have embraced your inner farmhand and are raising chickens yourself?

Xin speculates that these birds will perform about the same as the free-range type, in terms of feed utilization and carbon footprint. However, as many suburban hen-keepers note, backyard birds can become important parts of your home's ecosystem, performing useful services such as pest control, food waste disposal and compost turning. Plus, you don't have to worry about transportation-miles-to-store issues -- making a homegrown hard-boiled egg the ultimate locavore treat.

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