Double yolk in a chicken egg - a disease or not

Double yolk eggs are not a medical condition that calls the veterinarian urgently, it is enough to understand the chicken's reproductive system.

First, double yolk eggs are common in young layers that have just begun their laying cycle (found in pullets between 20 and 28 weeks of age). It is especially common in pullets of productive egg breeds such as white leghorn or broken brown. Young hens may have multiple ovulations because their reproductive systems are not fully synchronized. This is why you are more likely to get double yolk eggs from laying hens early in their egg journey.

Ideally, a hen's ovary releases one yolk into the bird's oviduct, which occurs about an hour after the last egg is laid. However, an overactive ovary and hormonal changes can cause double secretion, whereby the hen's ovary will secrete two yolks at the same time and they will remain in the same shell during egg development. Incidentally, according to the Guinness Book of World Records, in July 1971, a woman named Diane Hainsworth from the Hainsworth Poultry Farm, New York, usa , reported an egg containing nine yolks!

Heredity also plays a role. Hens prone to producing double yolk eggs can pass these traits on to their offspring, scientists believe that double yolk is an inherited trait, such as in Orpingtons. 

In some countries, such as India and CHINA, chickens that lay two-yolk eggs are valued and bred specifically for this trait. But getting two-yolk eggs from one laying hen on a permanent basis will not work, if it were possible, then the egg industry has long put such breeds and eggs on stream. Double yolk eggs are not normal, and due to their large size (such an egg is twice the size of a normal one) can be harmful to the HEALTH of the laying hen. 

Modern chickens are more likely to lay double-yolk eggs than in the old days, when this was a whole event, also due to highly nutritious feed and artificial lengthening of daylight hours. Exposure to light has a direct effect on egg production. Not surprisingly, some poultry farmers use artificial lighting to increase egg production, for example from 8 o'clock to 16 o'clock. An abrupt change in light duration often results in double yolks even in adult layers. 

Can twin chicks hatch from this egg? Hardly. In cases where two chicks are formed in a fertilized egg, one dies first because the embryos are essentially competing with each other, and the stronger of the two survives. The second chick generally does not survive to hatch either.

Otherwise, two-yolk eggs are just as nutritious as regular ones. And as soon as the reproductive system of pullets returns to normal, you will collect eggs with one yolk. 

Of the miracles that the reproductive system of chickens can present, one can also note the egg in the egg. Like a double-yolk egg, this one will also have two yolks, but they are separated from each other: it turns out an egg inside another. This anomaly occurs when the first egg in a hen's body moves backward instead of forward. There it combines with another yolk and protein and moves in the right direction, getting another layer of shell.
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