Do commercial chicken's eggs contain B12?

Question

If chickens are fed with only treated grain, where do they obtain vitamin B12 from? Are these eggs a good source of vitamin B12?

Answer 1

In nature, poultry get their B12 by pecking for insects and worms in the dirt. Since this behaviour is not possible on industrial farms, B12 is added to animal feed¹.

According to the USDA, one cooked egg (50g) contains 0.56µg of vitamin B12². The recommended daily intake of B12 for people age 14 and older who aren't pregnant or breastfeeding is 2.4µg³, though the FDA uses a higher RDI of 6µg for nutrition labeling⁴. At 9.3% of the FDA's RDI for B12, eggs do not meet the definition of a "Good Source" of B12, which requires 10-19% of RDI⁵.

When I personally consider what would be a "good source" of a particular nutrient, I am also interested in factors such as the foods other health effects, it's environmental impacts, and more. Wikipedia provides an overview of health concerns, and farming conditions for eggs.