I hustled out to the coop — the girls were staying in, due to snow and cold — and knelt beside them to get a birds-eye view out their door. Nothing unusual. Then I turned to look at the nest boxes and beheld the cause of their cackling: a perfect green egg, the first laid by my little pullet-turned-hen Ellie.
Ellie is a particular kind of chicken mutt known as an Easter-egger or Americana, for their characteristic blue- or green-shelled eggs. The novelty makes the birds popular with flock-keepers, and her eggs are bound to make Ellie — a pretty bird with rust-tinted grey plumage and smoky ear muffs — a favorite among friends who share in my flock’s bounty.
A chicken egg is surely the least appreciated of all agricultural “commodities,” as we humans are wont to classify the animals we eat and their byproducts. Scrambled, fried, soft-boiled or poached, eggs are the most ordinary of breakfast staples. But the process by which they come into being requires an elegantly choreographed physiology.
For reasons not fully understood, only one of a hen’s two ovaries — the left — matures, perhaps because her body cavity has room for only so many developing eggs. A single ovary contains thousands of germ cells, each capable of becoming an egg, though most will remain quiescent.
Those that awaken begin their journey to eggdom with the help of follicle cells, which enable the accumulation of yolk from material synthesized by the liver and released into the bloodstream. At any given time, the ovary of a hen who is actively laying will contain many small follicles and also a number of variably larger follicles which are putting on yolk in progressive order, anticipating the sequence in which they will eventually be laid as completed eggs.
I observed this graphically a few years ago in one of my young hens who stopped laying, fell ill and then died mysteriously. A veterinarian friend volunteered to do a necropsy, which revealed within the hen’s ovary a virtual army of potential eggs that would never be. The lower part of her oviduct — the avian equivalent of a fallopian tube — was obstructed by a waxy white material that signaled salpingitis, the infection that had caused the hen’s death. It was a sorry thing to see: not just the life gone from my glossy red hen laid open on that stainless steel table, but her fecundity — all that possibility — forever ended.
In a healthy hen, the oviduct is a sort of combined conveyor belt and assembly line, though the mechanical analogy does violence to the peristaltic poetry and exquisite timing that complete what the ovary started. Muscular contractions move the developing egg along as it acquires, in turn, albumen (the “white”), shell membranes and finally — during a stay of some 20 hours in the shell gland — the shell itself. Brown pigment is a coating applied to the last shell layer, and is due to molecules known as porphyrins, which are related to hemoglobin. Blue pigment derives from oocyanin, a bile byproduct, and permeates the shell. Green eggs like Ellie’s result when a brown coating overlays a blue shell.
Whether a hen lays white, brown, blue or green eggs depends on her genes and, more generally, her breed — or in Ellie’s case, pseudobreed. But within the broad range of brown, blue or green, there is considerable individual variation in intensity and hue, and occasionally speckling.
None of which explains why my entire flock — which has been nonchalant about the arrival of other first eggs, all brown — was so excited by Ellie’s debut. Chickens have much better color vision than humans; perhaps that accounts for it. And, of course, they know what goes into making an egg.
The account of laying physiology within this post owes much to The Chicken Book, by Page Smith and Charles Daniel, an indispensable and highly readable addition to the library of any chicken -appreciator.