Double-Yolked Eggs – Twice the Fun in One Eggshell
Folklore imparts many meanings on finding a double-yolked egg. Some cultures believe that discovering two yolks in one eggshell is a sign of a coming pregnancy. Similarly, other superstitions suggest that a double-yolked egg found by a pregnant woman, means that she will give birth to twins. Other cultures impart darker meanings upon the double-yolked egg. For example, in Norse mythology the double-yolked egg is an omen of an impending death in the family. Overall, the double yolker is more often than not considered to be a symbol of good fortune.
Though only about one in one thousand eggs will have two yolks, the biological process behind creating a doubl- yolked egg is surprisingly simple. A typical hen ovulates a single oocyte (the ovum that ultimately becomes the egg yolk) approximately once every 18-26 hours. A released oocyte travels from the ovary into the oviduct, which is the long, sectioned organ in which an egg is essentially constructed. As the oocyte travels down through the oviduct, various layers of the egg (e.g. the albumen, the inner membranes, the shell) are added as the egg passes through the various sections of this organ.
A double-yolked egg is formed when a hen’s ovary has a hiccup by which two oocytes are released simultaneously (or within a couple hours of each other). The two released oocytes journey through the oviduct together and have the various parts of the eggs added over them as a single unit. Ultimately, the two oocytes are encased in one eggshell. Double-yolked eggs are typically larger and longer than their single yolked counterparts.
Typically it is younger pullets new to laying that produce double-yolked eggs. Their reproductive systems just have not yet gotten into a regular groove. However, as the hens age their systems usually regulate and stop releasing more than one oocyte at a time. Double-yolked eggs are more commonly found in heavier breeds of chickens (e.g. Rhode Island Reds) or breeds that are particularly good layers (e.g. Leghorns). Sometimes, the double-yolked egg phenomenon is caused by a genetic anomaly and a hen with such genetic traits will lay double yolkers throughout her life.
You can learn more on the process by which chickens form eggs in episode 030 of the Urban Chicken Podcast LINK HERE.
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