I recently bought a carton of a dozen jumbo brown eggs. Of the 5 I’ve eaten so far, all are double-yolked. Which got me to thinking …
What is a double-yolked egg biologically? Is it simply the equivalent of fraternal twins in mammals? Given that mammal twinning is something that happens post- fertilization, I don’t think it’s quite as simple as that.
And the real question … If these eggs had been fertilized what would have happened? I have a hard time imagining two sucessful chicks in an inflexible space designed for one. Do you get one aborted chick & one sucessful one, or is the egg usually a total loss?
How common are double yolks in commercial egg farming? When I buy large or extra large it seems like about 1 in 75 to 1 in 100. It makes some sense that double yolks would be more common in jumbo eggs because after all, the jumbos are exactly those eggs which are much larger than average, and that second yolks has got to take up some space.
But I’ve eaten jumbos for years & never had a carton full of them. Any chicken ranchers care to give a thought to this?
<blush> Q the M remembers me! I have arrived at the SDBM
Strangely, this is the second thread about double yolked eggs in the space of a month.
Here’s my post to that previous thread, reprinted because I’m lazy.
Double Yolked Eggs
Double yolked eggs can be considered maternal twins, the result of a double ovulation. Fraternal twins are basically impossible (if you really want to know why I think so, ask. Otherwise I’ll skip it for now because it’s complicated).
Two yolks in one egg are more common for young hens whose reproductive systems are going like gangbusters, and older hens who have a genetic predisposition towards large eggs.
Hens ovulate about once a day in response to hormones, but the hormonal release is light controlled. Long daylight hours stimulate the hormone release from the brain, and the fluxuating levels cause ovulation similar to humans. Although chickens and most other birds only have one ovary, that ovary is covered with yolks that are waiting to be ovulated. It looks like a big cluster of yellow grapes. If a yolk is at the right stage of development when the right sequence of hormones hits, then the yolk is ovulated. The yolk then travels down the fallopian tube and uterus, where the egg white, membranes, and shell get added.
Young hens, like young women, have ovaries that are full to bursting with developing eggs. When the ovulation hormones hit, they often have two yolks (or eggs in humans) that are ready to go. Both eggs travel down the fallopian tubes and uterus together and end up stuffed into the same shell.
Older hens who have a genetic predisposition towards large eggs are a little slower reproductively. Older hens lay bigger eggs than young ones anyway because their bodies are more used to the process. However, it takes time to add all that egg white. Because the ovulation cycle is slightly more than 24 hours, and finishing an egg completely takes another 24-26 hours, there can be overlap, and the hen might ovulate again before the first egg is completely finished. When that happens, she might decide to deliver the first egg prematurely, and you get a floppy egg thing with a thin calcium outside, or she might stick both yolks in the same shell. It just depends on how close together things happened.
All commercially produced eggs are sorted using a machine. The hand technique hasn’t been used since my grandmother’s time. The eggs are collected and placed in a big flat, and then backlit. A person looks over them all over and touches any problem eggs with the point of a special wand. The wand is connected to a computer in the ceiling, which calculates the egg’s position in the flat based on the angle the operator moved the wand into when she touched the egg. The operator can also tell the computer exactly why the egg needs to be pulled. The eggs then move down the fancy conveyer belt which reconfigures to move the marked egg out of line and into the appropriate collection basket.
Generally, producers don’t like to put double yolked eggs in with other eggs because double yolked eggs are taller and more oblong, so they don’t fit in the cartons and are prone to breaking. Since one broken egg means the other 11 don’t get bought, it’s worth pulling them out. Plus, producers can ask a higher price for double yolked eggs.
Double yolked eggs, and other strange but perfectly safe eggs like blood/meat spots and peewees, can usually be bought directly at the farm, if the farm has an on-site store. Most do.
Chicks started from a double yolk rarely make it to hatching stage. As you found out, there just isn’t enough space and air and nutrients in there for two. Also, the process of hatching is pretty coordinated and would be screwed up for two. I’m curious, how do you know one died before the other?
The fact that the OP got a carton full of double yolkers is amazing. Either there was a mix up in the sorting, or the producer has his bar for extra jumbos set so high that he isn’t screening out the double yolkers well enough.
(And my answer to Pullet’s question was that I could see the hearts beating when I candled (shone a very bright light through) the egg, and one heart stopped beating before the other - several days in my more than 20 year old memory of a 10 year old, but maybe it wasn’t really that long.)
Yes, Pullet, you are famous here. When I posted I was hoping you’d stop by & give us the 100% Straight Dope on this.
We used another one from that carton today for baking. It too was double-yolked so we’re 6 for 6 in that carton. Today I got two more cartons of the same from our source - a Mom & Pop produce stand which gets them from a small, but still commercial source. It’ll take a week or so to eat them all; I’ll report back how many doubles we’re getting. Oh yeah, they’re $1.50 / dozen. Hurray for wholesomne, cheap, & lots of it.
I have seen cartons sold specifically as double-yolk eggs. I don’t buy them, because geez expensive, but sometimes you can buy them…same as you can sometimes buy ‘small’ eggs or even ‘pullet’ eggs, even in an ordinary grocery store.
The producer must not have taken a good look inside their eggs, then. And isn’t that like half the current rate for a normal dozen eggs?
Oh well. Double bonus for you!
