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For the first time I have seen hen eggs with two yolks.

Do they indicate a special kind of hen?
OR A special kind of grain fed to the hen?
OR Some scientific procedure which makes hens produce such eggs?

Are these kind of eggs safe to eat?

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3 Answers 3

up vote 13 down vote accepted

Double-yolked eggs are the result of an anomaly in the egg generation process in the hen.

They can happen in any breed of hen, on any feed. It is a result of two ova being generated at the same time, and then encapsulated in a single shell. According to My Pet Chicken, it happens more often with younger hens.

I am not aware of any process to intentionally foster double yolked eggs, but that doesn't mean such a thing doesn't exist.

They are safe to eat, although they may be visually startling.

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5  
Like twins in humans? –  TheIndependentAquarius Feb 16 '13 at 17:20
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In the broadest sense, yes, kind of like a situation that might possibly lead to fraternal twins in humans. There are many factors in each species, and mammals and birds are pretty different in the details--for example, the whole shell thing. –  SAJ14SAJ Feb 16 '13 at 17:22
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Rarely I (unknowingly) buy a whole box of double-yolked eggs, so it seems to me it's not always by chance. Can it be induced somehow? I don't remember anything particular about those boxes, but maybe you know? –  jkadlubowska Feb 16 '13 at 18:16
    
@jkadlubowska If you have enough egg production, they can be segregated by candling the eggs... –  SAJ14SAJ Feb 16 '13 at 18:37
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The way I heard it from my grandmother is this indicates very well-fed, healthy hens. It was very desirable, and hens laying these on regular basis were a serious bragging right. Such eggs were also considered more valuable as summarily they contained more yolk matter. –  SF. Feb 20 '13 at 9:46

A hen aged between 20-28 weeks has a one in a hundred chance of laying a double yoked egg. Since all the eggs in a box usually come from the same flock and all the birds in the flock are the same age, if you find one double yolk, the probablity of finding more in the box is high. As double-yoked eggs are larger than single yoked, if the eggs are graded to be the same size in a box, the probability of finding them increases.

http://www.bbc.co.uk/news/magazine-16118149

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According to my onetime teacher in Reproductive Biology at Oregon State University (Go Beavers!), Fred Menino, hens commonly lay multiple yolk eggs (I think the record is 9 yolks, but I may be mis-remembering) when young, before they are completely reproductively competent. To some degree this is a result of the selective breeding programs we (humans) have used to increase the numbers of eggs chickens lay in their most productive laying years, which favors hens that reproduce early in life.

So, to answer the question(s): Yes, it is a special sort of hen, bred for generations to lay huge numbers of eggs. It is not a special kind of grain; though the diets of commercial layers is very carefully chosen to maximize egg-laying, that just means getting the hens the closest to perfect nutrition for making lots of eggs. The scientific procedure is selective breeding for maximum egg-laying. This is very powerful. It's not "genetic engineering", but has results very quickly, and has been practiced since humans have been breeding animals for food and profit.

The eggs are as safe as any other egg.

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Yes, it is a special sort of hen, bred for generations to lay huge numbers of eggs. Please add sources to support your claims. –  TheIndependentAquarius Feb 21 '13 at 5:52
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This is the story of domestic animal culture. I don't think the claim is sufficiently outrageous to require citations--in fact it is completely reasonable. Just as we breed milk cows to give lots of milk, corn to give lots of grain, domestic chickens for laying have been bred to give lots of eggs. Daily laying is not a strategy wild birds engage in! –  SAJ14SAJ Mar 19 '13 at 3:15

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