Pasture-ized Poultry

"Grazing is good.” That could be a cow talking. But Heather Karsten, assistant professor of crop production and ecology, says that when pastures are managed carefully, the whole agroecosystem benefits.

chicken in bushes
Gwendolyn Crews

Healthy chicken: A laying hen forages for clover.

First of all, says Karsten, it's good for the soil. Grass holds soil in place and keeps it from eroding. Grass root mass is like a big sponge, absorbing and retaining water. And grass's roots are dying all the time, “putting more organic matter into the soil, which contributes to soil aggregation and better water and air infiltration, and to more diverse biological activity, nutrient release, and carbon sequestration,” Karsten says. “The most fertile soils around the world developed under perennial grasslands.

“From a human perspective, the animals are out there grazing their own forage, managing their own feed, and spreading their own manure, so there's not as much labor, equipment, storage facilities, or energy involved for the farmer. And grazing systems, if they're well managed, can be very profitable.”

From the animal perspective, grazing is good for nutrition. With careful pasture management, grasses can provide high levels of protein and vitamins.

Cows graze. Goats graze. Horses graze. Why not chickens?

“Animals with just one stomach, like chickens and people, don't have the digestive micro-organisms needed to get all their nutrients from pasture,” Karsten admits. But there are advantages to raising even chickens on grass, she insists. Poultry raised on fresh pasture instead of stored grain get more unsaturated fats and vitamins in their diets. “It's like the difference between fresh and canned vegetables. There are more nutrients available in the fresh,” she says. Pasture-fed chickens can also get bonus nutrients by eating grass-dwelling insects. And grazing chickens on a pasture that has already been munched on by ruminants helps with the break-down and spread of manure. The chickens' diet must be supplemented with grain, but Karsten thinks it could still be cheaper to raise chickens on pasture and grain than on grain alone.

Not all grasses are equal, however. “The leafier the plant, the higher the digestibility for
the animal,” says Karsten. If a pasture is overgrazed or the grass is too mature and “stemmy,” the nutritional benefits fall off. And in a recent study, Karsten and Ellen Seconi, a graduate student in agronomy, determined that legumes like alfalfa and clover are higher than grasses are in omega-3 fatty acids, which are thought to lower health risks including cancer, cardiovascular disease, and autoimmune disorders. Armed with this information, Karsten and Paul Patterson, associate professor of poultry science, set out to find the best pasture-plant species for optimal nutrition for the animal that could then be passed on to the human consumer.

Over a six-week period, Karsten, Patterson, and undergraduate assistant Gwendolyn Crews rotated 25 chickens from grass, to red and white clover, to alfalfa, grazing them for two weeks on each species. To facilitate rotation, they designed a mobile chicken coop with help from students from the Agricultural Systems Management Club. The coop, which could be trundled around the field on wheels, provided the chickens with food and water, protected them from predators, and served as a nest box. During each rotation, egg samples were taken and analyzed for levels of unsaturated fat and vitamins in their yolks. The researchers then compared eggs produced on each section of pasture to eggs taken from chickens raised in commercial cages on a typical grain diet.

They found that the pastured birds produced about three times more omega-3 fat in their eggs than did birds raised on an industrial diet. Regarding the best pasture mixes, “On average across all these periods, the mixtures highly dominated by legumes—clover and alfalfa—produced 18 percent more omega-3 fat than grass alone,” Karsten says. Eggs from the alfalfa pasture had 25 percent more omega-3s than grass-produced counterparts. “In absolute amounts, this was not a very big increase,” says Karsten. “But with more research and some different feeding regimes, it might go higher.”

Pasturing also boosted levels of vitamins A and E. “On average, we saw about twice as much vitamin E and 40 percent more vitamin A in the yolks of pasture-fed birds than in the caged birds. The longer the animals were on pasture, the more vitamins they produced,” Karsten says.

“From this study we confirmed three nutritional advantages of raising hens on pasture as compared to on an industry diet in cages: the increases in omega-3 fatty acids and in vitamins A and E. We also found that differences in omega-3 levels in plants have an effect on the eggs. And we learned how to manage chickens on pasture.”

Heather Karsten, Ph.D., is assistant professor of crop production and ecology in the College of Agricultural Sciences, 251 ASI Building, University Park, PA 16802; 814-863-3179; hdk3@psu.edu. Paul Patterson, Ph.D., is associate professor of poultry science in the College of Agricultural Sciences, 223 Henning Building, University Park, PA; 16802; 814-865-3414; php1@psu.edu. Gwendolyn Crews is a junior in agroecosystems with a minor in horticulture. Ellen Seconi is a graduate student in agronomy.

Last Updated May 01, 2003