Chickens make eggs through a remarkable biological process that takes about 24 to 26 hours per egg. Here's how it happens step-by-step:
- Yolk Formation and Release
The process begins in the hen's ovary, where thousands of immature yolks (ova) are present from birth. When a yolk matures, it is released from the ovary into the oviduct. This release takes about half an hour
- Fertilization (Optional)
If the hen has mated with a rooster, fertilization occurs in the first part of the oviduct called the infundibulum. If not fertilized, the egg will still develop but won't hatch into a chick
- Egg White (Albumen) Formation
As the yolk travels through the oviduct's magnum section, layers of egg white form around it over approximately three hours. The egg white cushions and nourishes the yolk
- Shell Membranes Formation
In the isthmus section, the inner and outer shell membranes are added around the albumen. This takes about 1 to 2 hours and helps give the egg its shape
- Eggshell Formation
The egg then moves to the uterus (shell gland), where the hard calcium carbonate shell forms over about 20 hours. Pigments may be added here, determining the shell color (white, brown, blue, or green depending on breed)
- Bloom (Cuticle) Application and Laying
Just before the egg is laid, a protective coating called the bloom or cuticle is added to protect against bacteria and moisture loss. The egg then exits the hen’s body through the cloaca (vent)
The entire process is continuous, with hens typically starting the next egg about 30 minutes after laying the previous one
. Not all eggs are fertilized, so hens can lay eggs without a rooster present. In summary, egg formation is a complex, finely-tuned process starting from yolk development in the ovary, moving through the oviduct where layers of white, membranes, and shell are added, culminating in the laying of a fully formed egg roughly every day
