A study by Penn State University researchers has shown that eggs produced by chickens allowed to forage in pastures are higher in some beneficial nutrients.

They examined how moving pastured hens to forage legumes or mixed grasses influenced hen egg omega-3 fatty acids and concentrations of vitamins A and E, and also compared the eggs of the pastured hens to those of hens fed a commercial diet. The differences were striking, according to lead investigator Heather Karsten, crop production ecologist.

“Compared to eggs of the commercial hens, eggs from pastured hens had twice as much vitamin E and long-chain omega-3 fats, more than double the total omega-3 fatty acids, and less than half the ratio of omega-6 to omega-3 fatty acids,” she says. “Vitamin A concentration was 38% higher in the pastured hens' eggs than in the commercial hens' eggs, but total vitamin A per egg did not differ.”

Seventy-five sister hens were assigned to one of three pasture treatment groups – alfalfa, red and white clover or mixed cool-season grasses. Groups of hens were rotated to all three pasture treatments, each for two weeks, and their diets were supplemented with commercial hen mash. Pasture botanical composition, forage mass, leaf-to-total ratio and plant fatty-acid composition were compared among pasture treatments. Eggs of the pastured hens were compared to eggs of 50 sister hens that were fed only commercial hen mash in cages for the entire six weeks.

“The chicken has a short digestive tract and can rapidly assimilate dietary nutrients,” says poultry scientist Paul Patterson, a co-investigator in the project. “Fat-soluble vitamins in the diet are readily transferred to the liver and then the egg yolk. Egg nutrient levels are responsive to dietary change. Other research has demonstrated that all the fat-soluble vitamins, including A and E, and the unsaturated fats, linoleic and linolenic acids, are egg responsive, and that hen diet has a marked influence on the egg concentration.”

Forage parameters in the study varied somewhat, Karsten concedes, but did not explain plant linolenic acid variation. Seventeen of the 18 quantified egg fatty acids and vitamin A concentrations did not differ among the three pasture treatment groups. Eggs of the hens that foraged grasses had 23% more vitamin E than eggs of hens that foraged clover. “Results suggest that grass pastures may enhance vitamin E in eggs of pastured hens more than clover,” she says.

The researchers note that the hens did not forage to the degree necessary to meet their requirements for energy and protein, when compared to the commercial birds. At the end of the experiment, pastured hens weighed 14% less and averaged 15% lower egg production than commercial birds.

“Pastured hens were lacking dietary protein and energy to match the intake of the commercial hens,” Patterson explains. “We have since estimated that, at the level of voluntary forage consumption of hens in this study, pastured hens would require additional mash feed to sustain body weight and egg production equal to that of the commercial hens.

“Supplementing the birds with additional mash, however, would likely result in reduced omega-3 fatty acid and vitamin A and E concentrations in their eggs,” he adds. “Further research is needed to identify how to optimize pastured poultry feed supplementation for optimum egg production, hen welfare and egg nutritional quality.”

Producing poultry on pasture or cover crops is becoming a popular way for livestock and crop farmers to diversify their operations in the U.S., especially the Northeast. Poultry are often rotated onto pastures after cattle or sheep, where they forage on regrowth and scavenge for invertebrates in manure deposits, often helping to distribute manure nutrients.