Have you ever wondered how an egg is made? Thanks to Sarah Mayhugh, a homesteader in Virginia, we have a wonderful visual to help you understand this process.
A female chick is born with thousands of ova on its ovaries, but not all of the ova will reach maturity. Unlike most female species, avian females only have one functional ovary. The hen is considered reproductively mature as early as 16 weeks of age. The ovary contains both immature and mature follicles. Each ova takes approximately 10 days to reach maturity. The egg-laying process begins with the release of the ovum from the ovary. The ovum is surrounded by the yolk, which is rich in protein, fat, and water and provides a food source for an embryo. From this point, it takes approximately 25 hours for the egg to reach complete development. A hen may have multiple eggs in various stages of development throughout her reproductive tract. When the yolk is released, it progresses into the oviduct, which has five distinct parts: the infundibulum, ampulla (or magnum), isthmus, uterus (or shell gland), and vagina. The infundibulum catches the yolk when it is released from the ovary and is the site where fertilization occurs if sperm is present. If the hen has been exposed to a mature rooster, the infundibulum stores the sperm in sperm nests and can fertilize eggs for up to 3 weeks after exposure. Fertilization does not have to occur in order for the egg-laying process to continue. The infundibulum then directs the yolk into the ampulla, which begins the formation of the albumen (egg white). The ampulla secretes approximately 40% of the albumen before passing the yolk into the isthmus. The albumen consists of four alternating layers that contain approximately 40 different proteins. The isthmus continues albumen production and also develops the tough membrane beneath the egg shell. This membrane is important for preventing bacteria from entering the egg. The translucent egg then passes into the uterus (shell gland) where the rest of the albumen and the calcium shell are developed. An egg’s pigment and outer cuticle are added when the egg passes into the vagina. The egg is fully formed at this point and passes into the cloaca to be laid.
As you can see in the image Sarah provided, this particular hen had multiple eggs in development. This allows a hen to lay approximately one egg per day! Surprisingly takes a lot of work to make one egg, doesn’t it?
– Virginia Tech: Dr. Wood and Dr. Tamim poultry classes