A doubled yolk egg occurs when two yolks are released (ovulated) at about the same time such that they are enclosed in the same shell. This happens about 0.1% of the time across a large flock but may never occur for any one individual hen.
The most common reason for double yolked eggs is that young hens, who are new to laying, haven’t completely worked out their egg production timing. As these young layers mature, their timing becomes more regular and they will release just one yolk at a time.
Another reason for double yolks is a late-in-life layer. When hens age and are nearly to the end of their laying season, their timing can once again get out of whack. Older hens may start releasing two, or even more, yolks at a time. If this happens, the hen may experience any number of health consequences as this can put her under a great deal of stress.
The last and least likely reason for double yolks is a hen that is genetically prone to ovulate two yolks in quick succession. There are no known breeds of chicken which are prone to double yolks but this does occur more frequently in hens from high production breeds or hybrids like “Production Reds”.
There is a lot more to learn about double yolks which you can check out in the soon to be released book “A Little Chicken Secret”. Please subscribe to our newsletter or to this site to stay up to date on the latest.