Many folks question what causes chickens to sometimes produce double yolks in their eggs, so here’s an attempt at the explanation.
To Understand What Causes Double Yolk Eggs You Need To Learn About Hens Reproductive System
A hen’s reproductive system (for more in-depth discussion click HERE) consists of an ovary and an oviduct. The ovary contains undeveloped egg yolks. The number of yolks (or ovum) that are contained here are the total number of eggs that the chicken can lay in her life.
These ova are released into the oviduct as each yolk develops. This usually occurs about an hour after the previous egg was laid. However, in young pullets and some heavy breed hens, two yolks are sometimes released within a couple of hours. These become double-yolked eggs.
Heredity can cause some hens or breeds to have a higher propensity for double yolks, but it most often occurs in pullets that are just beginning to lay (learn how we integrate them into the laying flock HERE). It takes a bit for their systems to “get-in-the-groove” of egg-laying. Typically, as hens mature, their systems settle down and they’ll produce one single-yolk egg approximately every 25 hours.
Are These Eggs Safe To Eat?
Yes, double-yolked eggs are safe to eat and are usually longer and larger than a single-yolked egg. The smaller, darker brown egg in the photo above is actually a jumbo-sized (2 ½ oz.) egg, whereas the light brown eggs are 3 1/8 oz. and 3 ¼ oz. respectively; and were both double-yolks.
Each time we’ve raised young pullets, we’ve seen a few double-yolked eggs. But as each group got older, they quit producing the double-yolked eggs.
Double-yolk eggs are not really that rare (about 1 in every 1000) but aren’t often seen in grocery store eggs today because commercial operations candle the eggs, separate out the double-yolks, and sell them to make egg-containing products.
If you are planning to incubate eggs for hatching, it’s generally recommended that double-yolk eggs NOT be included in the incubating eggs. Double-yolk eggs rarely hatch successfully.
I can remember when a double-yolked egg would occasionally turn up in store-bought eggs, but today they’re typically only found in backyard or farmstead raised eggs.
It’s too bad that we see them so rarely; I remember being told they brought good luck. At the very least, they’re a great curiosity for kids.