Sometimes you will find an egg that has two yolks, or a double yolk. I have even heard of some people finding three yolks–a triple yolk! Since I don’t have a rooster with my flock, my double yolks are just a special surprise in the cast iron skillet, but what happens if these type of eggs are fertilized?
If the double yolked egg happens to be fertilized, it is entirely possible for the chicken to hatch “twins.” In the same way, an egg with three yolks could possibly result in “triplets.” This is unlikely, however, since there is limited space and nutrients in the eggs to support more than one developing embryo.
Keep reading to find out why some eggs have more than one yolk and why it’s unlikely for them to produce a twin.
What Causes a Double Yolk Egg?
A double yolk occurs when a yolk is released a short time after another yolk has already been released during ovulation or if the first yolk is moving too slowly through the process. The two yolks will be encased in a single shell.
After a yolk is released from the ovary, it will travel to the magnum, which is where the egg white, or albumen is added. Several layers of egg white are added, although by the time we crack open an egg we can only see one egg white.
Once the egg passes through the magnum, it goes to the isthmus to receive the shell membrane and then the uterus for the shell to encase the developing egg. It is during this process that the two (or more) yolks must be together, otherwise they will not end up in the same egg.
Double yolks are considered an egg abnormality, which usually occurs in pullets that are just starting to lay eggs. Laying double yolks can also be an inherited trait found among some heavier breeds of chickens. I would occasionally see double yolks from my Barred Plymouth Rocks between the time they started laying (24 weeks) and about a year old.
How Many Chicks Can Fit in an Egg?
Usually double yolk eggs are longer, not necessarily larger. Steven describes these types of eggs as looking like limousines. These eggs are typically much longer than regular eggs and you can guess they have a double yolk before cracking them open.
Since the double yolked egg shells are not larger, this means approximately the same amount of space required to grow one embryo would be needed to grow two (or more). Egg shells are not flexible so they do not expand with the growing embryos inside.
If you have ever seen a chick hatch out of an egg, you know how crumpled up they are inside. Chicks hatch at 21 days and by day 20 they have filled the entire inside of the egg with their bodies. They are so tightly constrained in the shell that only their right eye is facing toward the egg shell where it can be exposed to light. Their left eye is tucked against their torso and won’t receive visual stimulation until after hatch.
Chickens, like people, can have a side of their body they gravitate towards using more often. Humans can be right- or left-handed. In the same way chicks that had their right eye facing the shell during incubation tend to prefer using their right eye when searching for food.
Another aspect of the egg to consider is that double yolked eggs do not necessarily mean double the nutrients. Eggs with more than one yolk usually have smaller yolks than regular eggs. Because of this, there would be decreased nutrients to feed developing embryos in case the eggs were fertilized. The yolks are so nutritious that chicks don’t need feed for the first day of life because they are still living off the nutrients from the yolk.
While eggs with multiple yolks are not uncommon, based on the tight space in the egg and lack of nutrients, it is unlikely for a fertilized double (or triple) yolked egg to result in twins (or triplets).
