Why do hens lay eggs with two yolksIMAGE CREDIT: freefoodphotos.com

           The yolk starts its journey as a follicle cell that is produced by the hen’s ovary in the process of ovulation. Once the follicle reaches the oviduct it is fertilized by the rooster’s sperm cells. As the yolk continues its journey down the oviduct, it is covered with albumin or egg white and at the lower end of the oviduct, egg shell is formed around the yolk.

           However in young hens which do not yet have a regular pattern for laying eggs, tends to produce eggs with two yolks. These hens sometimes produces two yolks in quick succession, which proceeds down the oviduct, where it is covered with albumin or egg white and a egg shell. Thereby two yolks gets entrapped in the same egg shell, thus producing a double yolked egg.

           Even though there is no particular breed that is capable of producing double yolked eggs, heredity can play a important role in the high production rate of double yolked eggs in some hens.

Such eggs are usually larger than a single yolked egg and are edible. Since there is not enough space for two chicks in a single egg shell, neither of the chicks survive during hatching.

          Sometimes there is breakage of non-follicle tissue from the ovary, which reaches the oviduct, where it gets covered with albumin or egg white and egg shell. This results in the formation of a egg with no yolk inside.


[1] http://www.enchantedlearning.com/subjects/birds/info/chicken/egg.shtml
[2] http://www.hindu.com/seta/2006/03/23/stories/2006032300061600.htm
[3] http://www.betterhensandgardens.com/2011/04/13/what-causes-double-yolks/
[4] http://www.mypetchicken.com/backyard-chickens/chicken-help/What-breed-of-chicken-lays-double-yolked-eggs-H189.aspx
[5] http://chickscope.beckman.uiuc.edu/resources/egg_to_chick/development.html