A female chicken is born with all of the ova (micro-yolks) her body will ever create stored in her left ovary. Although hens have two ovaries, only the left one is used in the reproductive process. The right ovary remains dormant. As a hen reaches sexual maturity, the ova develop and are released from the ovary, one by one, to begin the journey to becoming the recognizable egg that you see in the nest box every day.
The ova (egg yolk) is released from the hen’s ovary and swept up by the part of the oviduct known as the infundibulum. This is where the egg gets fertilized if your hen has been mated. The yolk contains the biological “recipe” to develop a baby chick, but it will only be possible if the egg is fertilized in the infundibulum. The yolk travels through this portion of the reproductive system in approximately 15 minutes.
The yolk leaves the infundibulum and progresses into the portion of the oviduct known as the magnum, where it resides for about 3 hours. During this time, the hen’s body is busy creating the albumen (or egg white) around the egg yolk and the chalazae. The egg white is 90% water and protein rich. As the yolk rotates, the stringy chalazae strands are created out of some of the albumen. The chalazae strands serve to anchor, stabilize and suspend the yolk in the center of the egg white.
The last section of the oviduct is called the isthmus and its’ main purpose is to add two shell membranes which enclose the yolk and egg white, forming the familiar egg shape. These two membranes provide the means for oxygen, carbon dioxide and nutrient exchange; as well as providing a layer of defense against bacterial invasion. This part of the egg production process takes roughly an hour and 15 minutes.
The shell-less egg finally leaves the oviduct tract and enters the uterus (aka shell gland), where it spends the vast majority of its’ time. The egg remains in the shell gland for 19-21 hours where the egg receives an additional albumen layer along with the calcium carbonate shell, the color pigment of the shell and an interesting biological film called the “bloom”.
The bloom is a protective coating that the hen’s body adds to the exterior of the egg shell just before it is laid. The purpose of the bloom is to create another barrier to potential bacteria invasion, but it also works as a lubricant during the laying process.
The egg does not require refrigeration as long as the protective bloom coat remains on the egg. However, if the protective bloom is washed off of the egg it becomes vulnerable to bacteria and will need to be refrigerated immediately. Never wash away the bloom if the eggs are to be incubated.
The color of the eggs your hen will lay is a product of the shell creation process and the porphyrin pigment on the shell’s surface.
Finally, the completely formed egg exits the hen’s body through the vagina and cloaca. The body rests for a VERY brief period of only 30 minutes and begins the process again by releasing another yolk from the ovary.
Learning how this incredible process occurs with such efficiency brings an entirely new appreciation for the backyard chicken owner’s flock and the incredible job they do every 24 hours to produce what is considered by many to be the perfect food. The incredible, edible egg. Give those ladies a big “thank you” when you go out to the coop to lock them in safely tonight.
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