So you want to know what color eggs your hen will lay? That’s easy: white. All chicken eggs are, in fact, white. Those dark, chocolatey-looking ones laid by a Maran? White shells overlaid with a paint, of sorts. You don’t even need to look at a chicken leg, because now you know.
Oh, but I know we love our brown “country” eggs just a little bit more, scientific reasoning be danged. I suppose the information could come in handy with bonus chicks or at farm swaps, but I understand this “leg” question as largely curious inquiry into a persistent agricultural myth, as catalogs are quick to educate prospective chick buyers on the color of each breed’s output.
What’s Leg Got to Do with It?
First, let’s look at what a chicken’s leg color does mean. In general, the leg—or shank—color is a genetic trait that is (spoiler alert) not directly related to egg color. Rather, it’s determined by a series of traits that interact, including plumage traits. There are, truth be told, a number of unknowns when it comes to chicken shank colors, though linkage to egg hue isn’t in one of these areas of uncertainty.
White, aka slate, legs are the wild type and determined by a dominant gene, known as “W.” Yellow legs, however, are determined by the recessive gene, “w,” and result from the consumption of carotenoids in foods such as greens and corn, an increase of which can, in fact, make the legs yellower. Yellow legs, however, fade over the course of a laying cycle as, in effect, the yellow is pulled out to produce yolks. Aging chickens lose pigmentation over the years, as well.
While white and yellow legs step the majority of barnyard struts, chickendom is a varied and sometimes strange kingdom. In terms of “exotic” leg colors, at least, dermal melanin contributes greatly to this diversity. Dermal melanin is present through a recessive gene known as (id+)—the absence of dermal melanin is dominant. The dark pigment is responsible for a rainbow of color variations, from the Bresse’s steel-blue shanks to the willow legs of Araucana. However, it’s not the underlying cause of the Silkie’s black legs. The Silkie’s shanks are determined by another dominant gene called fibromelanosis.
The Breed Tells You More
So while leg color doesn’t tell you what color eggs appear in the nesting box, there are some indirect links, considering breed type does dictate both. For example, an Araucana has willow-green legs and lays blue eggs (though the Araucana-like, mixed-breed Easter Eggers lay whatever color eggs they feel like), while a Rhode Island Red has yellow legs and lays brown eggs. Beyond breed-specific sets of traits, however, there’s no overarching link.
What Does Determine Egg Color?
So, what does make one breed of chicken lay a white egg and another brown? An old saying holds that white eggs come from white chickens and brown eggs from brown chickens, but I have a brown leghorn who would take umbrage with this claim. As mentioned at the top of this article, all chicken eggs are white, with brown eggs getting their color from a coating of protoporphyrin, a pigment derived from blood and applied to the egg shell’s more than 7,500 pores within the final few hours before laying time. Thirteen or more genes control not only the presence of protoporphyrin but also the amount applied, from the small amount for a light-tan Plymouth Rock egg to the maxed-out, cocoa-colored Maran’s egg. Time of year and hen age also affects the darkness of an egg. Seasons of heavy laying produce lighter eggs (there’s less protoporphyrin to paint on), while older hens just create less pigment.
So, what about green and blue eggs?
This is where I concede that my statement of all eggs being white was a bit overblown. Blue eggs are, in fact, blue through and through (at least the shells). It’s thought to be the result of a retrovirus that, somewhere along the line, inserted a gene called called oocyan. The eggs get their blue hue from the absorption of a bile pigment during interuterine formation. And green eggs are just blue eggs with a coating of protoporphyrin over top. But really, if it weren’t for that retrovirus, you’d be looking at a white egg.
Egg Quality Is Colorblind
Finally, I have to ask: Why are you so interested in egg color? Perhaps the query was purely scientific, but might I detect the faintest hint of judgment in the question?
There’s a longstanding piece of misinformation holding that brown eggs are healthier than their white counterparts, and this claim should be put to bed once and for all. Healthy eggs come from healthy chickens, regardless of shell color. A carton of grocery-store “country eggs” is arguably less desirable than eggs from a flock of Leghorns allowed to roam freely, eating grass, bugs and a ration of hand-mixed, all-natural feed. Leg colors are certainly interesting, but the egg is what really matters.