How do chickens lay eggs?

Hens lay no more than one egg per day as the process of laying an egg is governed by the presence of sunlight. The lack of natural light during the winter months means that even fewer eggs are laid during this time of the year. Humans can, however, ‘trick’ chickens into laying despite the limited sunlight by adding artificial light (such as a light bulb) to the coop.

The laying process starts when light entering the hen’s eye activates a photosensitive gland (the pineal gland) positioned nearby. Once stimulated, this gland triggers a process that leads to the release of an egg, or oocyte, from the hen’s ovary. An egg can still be laid whether or not it has been fertilised by a male, but only fertilised eggs can develop into chicks.

The orifice through which the egg leaves the hen is called the vent. Though this hole also forms the outlet for waste by- products (ie urine and faeces), there is a valve called the cloaca which separates the oviduct from the intestine.