Whats in an Egg?

It’s something you don’t think about all that often.  You go to the fridge, grab what you need, crack ’em and try not to get any shell into the slimy, sticky goop that comes out. 

The parts of an egg. The Chalazae are twisted because the egg rotates inside the shell membranes as it progresses past the infundibulum....natures version of "cats cradle"

Most people never really consider what is in the bowl or pan beyond that.  That’s sad….because the egg is really an amazing piece of engineering.  It only takes 22 hours to produce, it is impressive nutritionally, it is a source of both vaccines and medicine, AND it comes with a handy carrying case!

With today’s highly efficient strains of laying hens, an egg per day is not far from the truth.  This means that each day, the hen takes the most dominant follicle, wraps it in pure, digestible protein, water and membranes, then protects it inside a shell, and delivers it into the world.

The hens reproductive tract, with the parts labelled. The ovary makes ova (yolks), which then are covered during the 22 hourr trip down the reproductive tract

The ovary makes ova (yolks), which then are covered during the 22 hour trip down the reproductive tractThe infundibulum actually “plucks” the yolk off the ovary, and holds it for about 15 minutes. It’s here that fertilization will occur, if it is going to.  Then the 13 inch long magnum adds the thick albumin over about 3 hours.  In the isthmus, membranes are added which act as the scaffolding for the shell to grow from.  This takes about 75 minutes.Water is also added to the egg once the membranes are in place, in order to “plump” out the egg, and make it, well….egg shaped.  Then the egg sits in the shell gland for about 18 hours before being laid very quickly…usually just after daybreak. The addition of water is important, or you can end up with wrinkled eggs….the shell just covers the membranes, which are thin and pliable….without being plumped out, you get this :

I use this as a sign of stress in a laying flock.

You can get this type of thing from some diseases that injure the uterus, or if there is something that makes the egg leave the isthmus area too quickly.  During this relatively short period, an amazing package has been developed.  As someone who a) has kids and b) is in training, and wants to lose some weight as well as build muscle, I am acutely aware of the low calories and high protein available in the egg.  Eggs are still considered the yardstick against which other proteins are measured against, with beef getting a rating of .93, and whey protein has .25 of the quality of protein in an egg.  I also find it easier to get a scrambled egg into the kids than almost any other “healthy” food…(there is some debate in the house as to whether macaroni and cheese ranks as “healthy” food or not….).  For the low cost of 70 calories, eggs contain 6g of protein and 5g of fat.  They have an alphabet soup of vitamins, and iron, selenium and choline.

See....Lots of good stuff, and only 70 calories

See….Lots of good stuff, and only 70 caloriesThis is the breakdown of a “normal” egg.  If you feed chickens special things, such as lutein, Omega 3 fats, extra vitamins and potentially other things, you can harvest them from eggs, which make them the leading edge of the science of neutraceutical development.  Preventing macular degeneration, improving brain development and providing extra nutrition to people who don’t consume much food (think ill people, or the elderly) are all functions of eggs right now…the future has lots of potential.The other thing that is a nice characteristic of eggs is the versatility they have for preparation.  Hard boiled, over easy, quiches, scrambled, poached….all are quite different from each other, and eggs pick up the flavour of whatever you cook ’em in.  All in all, not a bad piece of food technology.  There are times, however, when you feel an urge to be a “purist”, and get back to nature….there is only one way to appreciate ALL the characteristics of eggs….not for the squeamish, however… 

Hard-Core Egg Consumption.....not sure what the health department would say...

Mike the Chicken Vet

9 responses to “Whats in an Egg?

  1. Nice information Mike. Perhaps you can explain why it is that some breeds can produce an egg in 22 hours and others take much longer. For instance we have marans and the longer it takes for the egg to be produced, the darker the brown colour of the shell. The marans are a little unpredictable, but there are other breeds that might typically take 26 hours to produce an egg. I just accept that it’s a fact, but I would be interested to know what controls that.

    • The short answer is genetics. Laying hens are very “selectable” for different traits. By selecting commercial breeds for better production, early breeders actually selected for shorter laying cycle and larger clutch sizes (a clutch is a group of eggs that are laid in succession, without a day off). Marans are dual-purpose birds, selected for both meat and egg characteristics. This means that the egg laying performance hasn’t been as developed as the commercial breeds. It is interesting about the darker colour coming from the “slower cooking” eggs….in commercial breeds, if an egg stays too long in the bird, an extra layer of calcium is added to the outside of the shell, resulting in a pale brown egg, which is less desirable. Likely Marans are less efficient at mobilizing calcium as well. Probably the differences between the birds would fill a book.

  2. Mike. Very informative post. An egg sure is a pretty amazing food technology.

  3. This is from memory, so don’t quote me, but I think the nutritional value (based on NuVal’s 1 – 100 rating system) of boxed macaroni and cheese is a 4.

  4. Thanks for this post. I’ve been getting a misshapen egg, like the one pictured, off and on for a few weeks. I recently thought I had a case of infectious bronchitis, but I have not had a overall drop off in production (my flock consists of 19 layers averaging 13-14 eggs a day now that temps are increasing). If IB is as intensely contagious as it is made out to be, I’d think I would have seen flock-wide signs by now. Perhaps it is just age/stress in one isolated hen…

    • Hi Deanna;

      I would make sure that you have enough calcium available for the hens. Often, wrinkled eggs are caused by eggs being held in the shell gland too long because of muscle weakness that is the result of low calcium. Have oyster shell, large particle limestone, or egg shells available to whoever wants it, and it may help clear up your problem. From what you say, I would be surprised if it was a bronchitis infection, since there has been no drop in egg productions, which is a pretty normal result of bronchitis.


      • Mike, your quick response is very much appreciated – thank you! I’ll heed your suggestion, and I’ll be sure to let other flockster friends of mine know about your blog. Thanks again!

  5. Thanks for the great blog. We are having trouble with one of our hens. She has been passing some type of tissue masses. Earlier this week we found several tissue masses in what seemed like a soft-shelled egg. Now she is passing tissue in her droppings. The masses consist of white tissue, seem to be multilayered, are quite firm and sized similar to a pea or small blueberry. She had tissue hanging from her rear yesterday. She didn’t seem bothered at all. We cleaned her up and she went on her way. She doesn’t seem to be in any distress otherwise — tail up, eyes clear, normal respiration, eating/drinking, etc. Do you have any ideas? We live in Dallas and it’s been difficult to find a vet who has any experience with hens. Any help would be much appreciated!

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