UNIVERSITY PARK, Pa.—Chickens allowed to forage in pastures produce eggs with more omega-3s, vitamin A and vitamin E compared to their commercially fed counterparts, according to a study from the Pennsylvania State University (Renewable Agriculture and Food Systems (2010)25:45-54). These added nutritional benefits may help justify the increased costs U.S. farmers charge for pastured poultry eggs, according to the researchers.
Compared to eggs of the caged hens, pastured hens' eggs had twice as much vitamin E and long-chain omega-3 fats, 2.5-fold more total omega-3 fatty acids, and less than half the ratio of omega-6:omega-3 fatty acids (P<0.0001). Vitamin A concentration was 38-percent higher in the pastured hens' eggs than in the caged hens' eggs (P<0.05), but total vitamin A per egg did not differ.
At the end of the experiment, pastured hens averaged 15-percent lower hen-day egg production than caged birds (P<0.0001), and weighed 14-percent less. The researchers noted with adequate supplements to meet their dietary energy and crude protein needs, hens on pasture will produce as many eggs and be the same weight as commercially fed chickens.
They used a cross-over design to compare pasture species: 75 sister hens were assigned to one of three pasture treatment groups: (1) alfalfa (Medicago sativa L.), (2) red and white clover (Trifolium pretense L. and Trifolium repens L.) or (3) mixed cool season grasses. Groups were rotated to all three pasture treatments, each for two weeks and supplemented with 70 g commercial hen mash bird. 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. Seventeen of the 18 quantified egg fatty acids, and vitamin A concentrations did not (P<0.05) differ among the three pasture treatment groups. However, eggs of the hens that foraged grasses had 23-percent more vitamin E than eggs of hens that foraged clover (P<0.0001).
