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How a Chicken Makes an Egg
You reach into the nest box and wrap your fingers around a warm, just-laid egg. You pick it up, feel its warmth against your cheek, and then pop it into in your pocket. Back in the house, you heat up the fry pan and crack open your egg, staring at all of its curious parts and poking at the yolk with a spatula. This egg came from your happy hens; unhappy hens do not lay eggs so you must be doing something right. The yolk breaks open from the spatula’s weight and spreads into the egg white. As it cooks, you wait patiently. When it is ready, you put it on a plate and serve yourself a fresh, egg-a-licious breakfast. The taste, well, those words are best left to your own imagination. But what about the journey that wonderful egg took to get to your breakfast?
The egg starts with the yolk. It begins small and is surrounded by a follicle necessary to transport the nutrients and pigments needed. Once ready—filled with sufficient nutrients and genetic material—the yolk descends into the oviduct, traveling first through a funnel-like section called the infundibulum. This is where it gets fertilized by sperm, if any has been stored. Next it ends up in the largest oviduct section called the magnum, where the yolk connects to the white, also called the albumen.
The next stop on the yolk’s journey is the short, narrow isthmus, where the inner and outer shell membranes are added, the latter of which provides the foundation upon which the shell is built. The yolk and albumen spend seventy-five minutes in the isthmus. Once surrounded by the inner and outer shell membranes, the group continues on to the shell gland, where the shell gets added, hardens, and changes pigment color and where the albumen’s four layers unfold. The egg spends more than twenty-four hours in the shell gland. Finally, the last layer, a thin protein mucus called the cuticle or bloom, seals the egg’s pores to prevent invasion by bacteria. Now the egg is ready to be laid.
The egg is formed inside the hen with the small end facing downward. It flips around just before it is laid so that it leaves the hen large end first. The egg passes through the vagina and out through the cloaca or vent. If needed, a hen can hold onto an egg until a favorable place or situation to lay it. This is key for a wild hen avoiding a predator. In this rare circumstance, it is possible that a hen will lay two eggs within a twenty-four hour period. Whew! It takes all that to lay an egg. To all the hens in your coop: Take a bow. They have earned it!
