One of the top questions we receive here at the Egg Nutrition Center is whether the nutritional profile of an egg is influenced by the housing conditions of the hen, particularly free-range versus caged. It’s a reasonable question to ask. Free-range hens may forage for bugs and plants, which could conceivably alter the nutritional intake of the hen and hence affect the nutritional content of the egg. It has also been questioned whether certain housing systems affect stress levels of the hens that may in turn, lead to changes in the nutrient content of an egg.
A recent study conducted by researchers at the USDA evaluated the nutrition content of eggs from hens raised under five different housing systems (including caged and free-range). They also looked at the impact of the strain and age of the hen on nutrition quality. In their first published paper from this study, they report on the mineral content of eggs of these different conditions.
The results are consistent with those of other studies such as Anderson et al., 2011 and Giannenas et al., 2009: age of the hen, the strain of the hen, and the conditions under which the hens are raised can result in small differences in the mineral content of the egg, but they aren’t a meaningful difference.
For example, the present study showed that concentrations of calcium and copper were 7 and 8% higher, respectively, in white hens (that lay white eggs) than in brown hens (that lay brown eggs). Manganese concentrations were 11% higher in 44-week old hens than 88-week old hens. However, there were no differences in any of the minerals tested between caged hens and free-range hens.
What do these results mean in terms of human health? Very little. In fact, the authors say it best:
“Despite statistical significance, differences in egg mineral content in our study were of such a small magnitude, that they are unlikely to be highly relevant to human nutrition”.
Put into practical terms, the 7% increase in calcium in the egg from the white hen is an incremental 8.5 mg per large egg compared to the egg from the brown hen. The RDA for calcium is 1,000-1,300 mg/day, depending on age and sex. While every little bit counts, there are numerous other foods that contain much more meaningful amounts of calcium that would contribute more significantly to meeting recommended intakes.
Levels of other nutrients (e.g., vitamins) were not reported in the present paper. However, others have failed to detect differences relevant to human health in these outcomes either.
These results add to the existing scientific evidence that the nutritional content of an egg is the same regardless of color or how the hens are raised. The notable exception is hens that are provided nutritionally-enhanced feed, which does result in higher concentrations of certain nutrients within the egg.