Hatching Science Center
Egg Size and Color
Egg size will vary based on the breed of the hen (some breeds just lay bigger eggs than others), the health and nutrition of the hen, and the age of the hen (older, more mature hens will lay larger eggs).
As hens mature and age, their eggs get larger. Though it is difficult to measure the pain of chickens, there is little evidence to suggest that hens experience any pain when laying, so it is unlikely that hens that lay larger eggs suffer more pain than their younger, smaller egg-laying counterparts. It is just part of their biology.
Sometimes people try to equate a human woman in labor to a chicken laying an egg, but there are significant differences in the size ratio and the anatomical passages and physiological processes involved in the two distinctly different systems of procreation. For greater detail on the reproductive tract and process of a chicken, access teaching and learning resources from Virtual Chicken.
According to the US Poultry Association, "Egg laying hens are not given hormones. Some egg cartons say that the eggs are hormone free; however, this is true for all eggs in commercial egg production in the United States." Find out more here.
There is only one thing that determines the color of a chicken's egg: genetics. All chicken breeds come with their own color of eggs—from white and brown to the more exotic greens, blues, and pinks. For more information about colors of eggs, see a list of breeds and pictures of their eggs here.
The white eggs that are most commonly found in conventional grocery store packages most likely came from Leghorn breed hens. Large-scale production facilities use this breed because they are efficient at turning feed to eggs and they don't put on a lot of muscle mass like most other hens do. Leghorns also produce well indoors with limited light and in confinement.
Organic eggs can be white or brown or any other color as long as the hen producing them was given organic feed and meets all other standards for organic labeling. The choice to use brown eggs is more about marketing and creating a difference in the obvious appearance of the eggs than it is about any other production matter.
No, eggs are not bleached. If an egg is white, it is because the chicken that laid it always lays white eggs. Eggs for grocery store production are always gently cleaned and sometimes pasteurized, but the color is based only on the breed of the chicken and will remain the same.
The color of the egg does not affect the nutrient content or the flavor of the egg. However, the nutrient content of the egg can be affected by a hen's diet. Find out more from the American Egg Board.