Note: Several readers have requested posts on topics that have already appeared here – this is one of those posts that has been updated and republished.
Reproductive System Explained
A hen’s reproductive system 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 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. 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 Double Yolks Safe?
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 is actually a jumbo-sized (2 ½ oz.) egg, whereas the lighter brown eggs are 3 1/8 oz. and 3 ¼ oz.; and were both double-yolkers.
Double-yolk eggs are not really that rare (about 1 in every 1000) but aren’t often seen today because commercial operations candle the eggs, separate out the double-yolkers, and sell them to make egg containing products.
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 we see them so rarely; I remember being told they brought good luck. At the very least, they’re a great curiosity for kids.