How does my hen produce an egg every day?

Posted 16th January 2017 10:06am by

By Gaynor Davies

The humble commercial hybrid hen (our lovely ex-bat) has been designed and modified over the years to ensure peak egg production and consistency of yield.

Compared to her fancy breed cousins and broilers bred entirely for meat production, the commercial layer carries little spare flesh and concentrates all her energy into produce an egg every day. In the past all these ex-bats would be sent to slaughter at 18 months of age before changes in shell quality and decreased frequency of laying became apparent. We are now living in more enlightened times and hens are routinely re-homed into pet backyard homes to enjoy a well- deserved retirement (although only a fraction of the UK laying flock of some 40 million hens manages to achieve this happy outcome). Hens are now the sixth most popular pet in the country, which means there are lots of households out there getting lovely fresh eggs on a daily basis!

We thought you might be interested to know the process which leads to a hen laying an egg for your breakfast.

The laying process

Hens have only one functional ovary – the left one. The ovary contains follicles of differing sizes and maturity. When each follicle matures, it is called a yolk or vitellus. The yolk travels from the ovary into the oviduct. The first part of the oviduct is the Infundibulum, this is where the egg stays for roughly 15 minutes. If the hen has been mated this is where fertilization takes place. Beware! If you plan to breed from your girls it is important to know that sperm can survive in the oviduct for as long as four weeks.If you have a particular cockerel in mind as the desired husband, keep other boyfriends away.

The next part of the oviduct is the Magnum where the egg remains for roughly three hours. The white is generated here. Passing down the oviduct the egg reaches the Isthmus and remains for one hour while two membranes form around it. Next comes a 24-hour period inside the uterus – the shell is formed at this stage. The final stage is the cloaca. With the help of the hormone arginine vasotocin which induces uterine contractions the egg is laid.

How many eggs will she lay?

A hen in her prime laying period between 20 weeks of age (point of lay) and 78 weeks of age (end of lay) would be expected to produce around 300 eggs annually (she has periods of rest in her cycle when laying stops briefly). Happily the majority of hens continue to lay after 78 weeks. (See diagram below)

The humble hen egg is designed to be an ideal incubator and nursery for a growing chick embryo. The shell is porous – typically around 7,000 pores in the calcium carbonate shell allow air in to the embryo. For this reason it is not recommended that eggs are washed if floor-laid as bacteria can be introduced via this route. There are strict regulations governing egg production within the egg industry and eggs are not allowed to be sold as first quality if dirty or damaged in any way. Hens utilise their own stored calcium if their diet is deficient and need 4g of calcium to produce one egg.