Chickens lay eggs upon receiving light signals.
Believe it or not, the egg-laying process in a hen begins in the eye. Hens lay eggs only after receiving a touch of light, whether it’s the natural sunlight that enters a chicken coop or the artificial light that illuminates a commercial egg incubator. The light stimulates a photoreceptor gland near the hen’s eye, which in turn triggers the release of an egg from the hen’s ovary.
Brown and white chicken eggs.
Most chickens lay eggs almost daily, unlike other egg-laying animals, which only lay one egg every thirty days or so. The chicken also releases a small disk of material that surrounds the egg and provides nutrition. The hen’s uterus also fills with albumin, the slimy substance we know better as egg whites.
Meanwhile, a membrane forms around the inner wall of the uterus, sealing the egg, yolk, and albumen. Eventually, a mixture of water, salt, and calcium surrounds this membrane, forming a thin but structurally strong outer layer. This shell molds to the shape of the uterine wall, giving the chicken egg its distinctive shape. While in the uterus, the narrow end of the egg points down, but then it will rotate and be expelled from the wider end first.
Hens can lay eggs almost daily.
Once the egg is fully formed, the hen’s uterus begins to contract in an effort to expel the egg. The suppository descends through a vaginal canal into an external opening known as a vent. The vent is a common opening for both egg laying and waste removal, but a hen cannot perform both functions at the same time. An internal flap known as the cloaca keeps the vaginal canal and intestinal tract separate until an egg or stool reaches the opening. When a hen is laying an egg, the cloaca descends and blocks the intestinal tract.
Once the egg passes through the cloaca, it is carefully expelled through a series of muscular contractions that essentially go around the birth canal and cloaca in one place. Eventually, the egg is pushed through the opening and ideally lands intact on the ground. Many hens let out an audible cluck at this point, but designated egg layers rarely show other maternal concerns. These hens lay eggs every 24 to 36 hours at the height of their productive years, so individual eggs rarely attract their attention.
Once the hen lays a certain number of eggs, she may stop producing more eggs and enter an “incubation” stage, a maternal stage where the mother will sit on the eggs until they hatch. To prevent egg layers from hatching, newly laid eggs should be removed daily. Hens will lay eggs whenever they think they need more to form a proper brood. The egg-laying process continues regardless of whether the rooster provides enough sperm for fertilization. A hen cannot tell if an individual egg has been successfully fertilized or not.