By Matthew R. March, MNRD
Polk County Extension Agent

Raising backyard chickens can be a fun and enjoyable experience. Most local producers raise chickens for egg production to provide their families and neighbors with home grown heart healthy nutritious eggs. We tend to take for granted that our laying hens will produce eggs and give little thought into the complex and interesting reproductive structure of laying hens.

Before we go any further into a discussion on the hen reproductive system it must be stated that it does not take a rooster to be present to produce eggs. A hen will naturally produce eggs if feed, water, shelter, temperature, and light hour requirements are met. A hen is born with every ova (which will develop into full size yolks) she will ever need in her lifetime. Interestingly, a hen has two ovaries, but only the left one is functional and contains 3,600 to 4,000 ova at birth. The tiny ova are held in place by a stalk. Once the hen reaches maturity, the ova will systematically enlarge and develop one by one into mature ovum, which at that point are released from the ovary. At the time of release, the mature ovum is the full-size yolk of the egg and the rest of the reproductive system adds the egg white and shell. Only one mature ovum will be released at a time, approximately one a day. However, a double yolk egg is the result of two mature ovum being released at once.

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The ovum will now spend 25½ hours being transported through the sections of the oviduct until the time of laying. The first section is the infundibulum, which is funnel shape and catches the ovum after release. The ovum will only remain in the infundibulum for 15 minutes. Next the albumen (white part of the egg) is added in the Magnum section. It will take three hours for the albumen to be added. After the Magnum, the egg enters the Isthmus section for one hour and 15 minutes where the inner and outer shell membrane is added. The shell membrane protects the egg contents from outside contamination. The last part of the egg to be added is the shell which occurs in the uterus. This is the longest step in the process and the egg will remain in the uterus for 20 hours and 45 minutes. The egg is typically laid by the hen within 15 minutes of it leaving the uterus.

Next time you are in the chicken coop collecting eggs for your omelet, think of the complex process it took for the hen to produce that egg. It all started over a day ago, long before you even stepped inside the chicken coop.