Double yoked eggs

Does anyone know what causes double yoked eggs?
One of my Cream Legbars has started laying them regularly. Not sure which one yet.
It's a perfect shell but they're huge!

This is interesting https://www.thehappychickencoop.com/double-yolk-eggs-and-other-egg-anomalies/
My black pullet, Iris, laid a whopping 65g. egg for her first one, and it was a double yolker. After that she went back to a normal pullet-sized 42g. and is gradually building up, as one would expect.

I've no idea what causes it, but I used to have an enormous speckledy who laid double yolked eggs regularly, all her life (she was five when she died). She would come into lay in about April, lay maybe four or five double yolked eggs a week until September or maybe beginning of October, and then have a well deserved rest for the whole Autumn and Winter! Not sure while I kept pearl so long actually, as she was a pain in the butt! She would go to bed early, but would stand in the doorway of the henhouse then, and not allow the others in! A right bully! So, I'd have to go and take her out of the house, and literally hold on to her until the others got settled , and then put her back in! A "character", which is, I guess why I kept her!

A bit of a mystery why it happens. Though some people claim that they have hatched twins from such eggs I remain sceptical. This being the case then it can't be an hereditary trait as it could not be passed on. It's years since I've had one (from a Minorca). Certainly the eggs tend to be bigger which can't be good for the hen that lays them.

It should simply be a case of dropping two yolks at the same time into the oviduct. One should be a day less developed than the other so slightly smaller, but the ones I've seen both yolks appeared the same size so perhaps there is a bit more to it than that? it's usually pullets coming into lay that produce them and then resort to one yolked eggs, so your Legbar is a bit unusual I think Rick.

Cheers, I'm reasurred that your speckeldy handled it well LadyA and I expect that if this Legbar does keep producing them she will have a normal break in the winter like a sensible hen.
It may be just a passing thing. They all took a long time to come into lay from pullets so I suppose, in the scale of things, they haven't been laying long but they've cirtainly layed a couple of dozen each by now so they are far from being first attempts.
Will have to try to figure which one is laying the double yokers.

I also don't know what causes them, and I've never had one from my hens, but then their eggs could never be classed as large! I rrecently read about a mare who brought twin foals to birth and beyond, in fact they are now racing siblings, but this was in the USA and maybe they do things differently there! I know that usually they 'squeeze' (yet another euphamism) one embryo as two embryos are not that unusual, so a mare only gives birth to a single foal.

The past couple of days I've had 6 normal sized eggs from the 3 of them so, for the moment, seems to be back to normal.
Last week I did go the the effort of picking them all up to check them over - something that they are not keen on at all. Maybe the stress of it? I find it funny with CLBs that they are quite bold and fly up onto your knee/sholder if they think food is around. But as soon as they see hands moving to catch them they never squat like a brown hybrid would, just run away like their life depended on it.

Last week, Iris, my black hybrid, laid her first egg, a 65-gram double yolker, as I posted above. The yolks were both quite small, what you'd get normally in a pullet's first egg.
Two days ago, Daisy, the Buff Barred, the last pullet to come into lay, produced a softie.
Yesterday she laid a HUGE 76g. effort; (ouch!)

Which contained two yolks of a normal size for a pullet's egg.

Today she's produced a nice little 43g. egg. Obviously learning from her mistakes!
The big double-yolker was particularly surprising as she's a slim, lightweight little hybrid, only a bit heavier than Lily, who is tiny even for a leghorn. Also strange that two out of these four birds started their careers with very large double-yolkers.
Although their eggs are all lovely and I think there will be plenty of them, I'm surprised and disappointed that, apart from the leghorn's white egg, I shan't be able to tell them apart. They're all the same colour and shape, though I was told that at least one would lay a darker brown egg. How can three pullets as different as a grey laced bluebell, a fawny-brown buff barred, and a jet black bovans nera all lay identical eggs?




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On my screen there are two different colours - in addition to the white of course. Maybe they'll change as they get older. My Welsummer's eggs were never the same colour two days running!

That one's big all over! At least ours was stretched out long. One of our blue eggs is a bit more greenish than the rest and when Arial was laying hers were always speckled on the end (otherwise indistinguishable from a regular brown egg.)
I think there is some shade difference in your photo too and the double yoke egg would probably be darker if smaller - a bit maybe.