The difference between fertilized and unfertilized eggs comes down to whether a rooster has been involved or not. Hens do not need a rooster to lay an egg; they do so (almost daily) on their own simply according to light patterns. However, if a rooster does mate with a hen, the eggs she produces are fertilized and, under the right incubation conditions, can bear chicks. No rooster means zero possibility of the egg ever becoming anything more than that.
Chances are you’ve never eaten a fertilized egg, because nearly all eggs sold commercially are produced by hens that have not mated, says Lauren Cobey, media representative for the American Egg Board. When fertilized eggs are sold for consumption, there is no danger of eating a developing embryo, says Cobey, for a few reasons: All eggs sold in the United States as food must be refrigerated, a process that halts any growth inside the shell. Also, the interior of any egg intended to be sold as food must be inspected—accomplished by shining a bright light through the shell (called candling)—which highlights any irregularities, such as a developing chick. These regulations hold true whether the eggs are intended for a large chain like Safeway or for the farmers’ market. Eggs with irregularities never make it to retail and are destroyed.
Nutritionally, says Cobey, fertilized and unfertilized eggs are the same.
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