Funnily enough, the whole egg laying process begins with a small gland near the chickens’ eye. This tiny gland is light receptive and when it registers light (either natural or artificial), it triggers the release of an egg cell from the chicken’s ovary.
This egg cell travels to the uterus, where it will eventually grow into the egg yolk. Meanwhile, the chickens’ uterus gradually fills with a jelly like substance, called albumin, more commonly known as the “egg white”.
A membrane then begins to develop around the perimeter of the uterine walls, effectively sealing in the egg yolk and albumen. In time, a combination of calcium, salt and water rims this membrane to form a sturdy outer shell.Once the egg is fully formed, the real work begins. The chickens’ muscles will start to contract in an effort to release the egg, forcing the egg to move down the vaginal canal towards an external opening, called a vent.
This vent is also connected to the intestinal canal and is used by the chicken to expel waste. Mid-way through its journey, the egg will reach an internal flap, called a cloaca. The cloaca is like a valve, which only allows one canal access to the vent at a time. Once the egg reaches this point, the cloaca valve descends and blocks the intestinal canal.
Once the egg has almost completed its journey, the chicken will stand up and then lower its back end, which causes the vent to open as wide as possible.
The strengthening contractions essentially turn the chickens’ canal and cloaca inside out, forcing the egg to drop free onto the ground. Ta da! An egg has been laid.