Chickens are an integral part of human agriculture, supplying eggs that are a dietary staple worldwide. The ability of a hen to consistently produce eggs is a complex biological marvel. This process demonstrates remarkable efficiency in avian reproductive biology. Understanding how chickens lay eggs reveals the intricate coordination within their bodies that supports this daily production.
Internal Egg Development
The journey of an egg begins in the hen’s ovary, which contains thousands of ova, or future yolks, from the time the hen hatches. Once a yolk matures, it is released into the infundibulum, the first section of the oviduct. This muscular funnel engulfs the yolk, and fertilization, if it occurs, takes place here within 15 to 30 minutes.
The yolk then travels into the magnum, where the albumen, or egg white, is added. This process takes three hours as proteins are secreted around the yolk. Following this, the developing egg moves to the isthmus, where the inner and outer shell membranes form around the albumen and the egg begins to take its oval shape, a stage lasting one hour.
The egg then enters the uterus, also known as the shell gland, where the hard outer shell is formed over 20 hours. Calcium carbonate is deposited, and shell pigmentation is added during the final hours in this section. Before the egg is laid, a protective layer called the bloom or cuticle is applied in the vagina, sealing the shell pores and helping to prevent bacterial entry. The entire internal formation process takes between 24 and 26 hours.
The Laying Process
As the egg fully forms, the hen prepares for oviposition, the act of laying the egg. One to two hours before laying, the hen exhibits pre-laying behavior, becoming restless and seeking a secluded nesting spot. She may explore various nest boxes, rearranging nesting material to create a comfortable hollow.
Once settled, muscular contractions within the oviduct and cloaca expel the egg. These contractions push the egg, blunt end first, through the cloaca, the common opening for reproductive and excretory systems. The actual expulsion of the egg lasts less than a minute. After laying, the hen may vocalize with a characteristic “cackle” and then leaves the nest.
Factors Influencing Egg Production
A hen’s egg-laying capacity is influenced by several factors, with light exposure being a primary environmental trigger. Hens require at least 14 hours of light per day to stimulate their reproductive hormones, with 16 hours leading to peak production. A decrease in daylight can lead to reduced or ceased egg production.
Proper nutrition is important, as hens need a balanced diet rich in protein (16-18%) and calcium for strong eggshell formation. A calcium deficiency can lead to soft or brittle shells and even egg-binding issues. Age and breed play a role, with hens starting to lay at 18-22 weeks and reaching peak production at 30 weeks, though production gradually declines with age.
Health and stress significantly impact egg output; diseases, parasites, and environmental stressors can reduce or halt laying. It is also important to note that hens do not need a rooster to lay eggs; they will produce unfertilized eggs regardless, but a rooster is necessary only if fertile eggs for hatching are desired.