biology zoology blog benno meyer rochow eggs

Chicken Eggs

Is there anything you did not yet know about them?

We used to keep chicken in New Zealand and it was my job every morning to collect their eggs and turn them into fried or poached eggs, boil them hard or soft, or serve them as scrambled eggs with some chives added to them. At that time, I frequently came across some abnormalities which excited my children (but not my Indian Brahmin wife, who never consumed eggs, fish or meat). Most interesting to them were the occasional eggs with two egg yellows, but even though all this happened many years ago, I remember all of the exceptional eggs I came across at that time. This morning, however, I had an egg with an abnormality I’d never seen before. The egg (like all fresh eggs do) sank nicely to the bottom of the pot, was boiled for 5 min, held briefly under cold water and then carefully de-shelled. You’d normally find an “air space” on the egg’s blunt end, but in this egg the air space was under the egg’s “equator”!

It was this incident this morning which made me look up some of my old notes on egg abnormalities that I (and others like a 19th century character with the beautiful name Wilhelm v. Nathusius-Königsborn) had encountered when studying eggs and their shells. First of all there is the egg’s shape, which can vary from almost spherical to torpedo-shape, but usually is -well, ‘egg-shaped’. I loved the occasional egg with a wrinkled appearance as if it had gone through the washing machine, but my children felt it was too odd and avoided it. I, on the other hand, felt these eggs were particularly tasty. Once I had a longish egg with no bilateral symmetry that looked as if bent. And then there is, of course, the occasional egg with little sand-like protrusions, i.e. calcium carbonate pimples on the shell’s surface. After the war (WWII that is) and not from our chickens, I had once received an egg with no hard shell at all, a case that suggests the hen had received insufficient (or too much) calcium or was stressed. However, if fresh and there’s nothing wrong with them, such eggs can be eaten just like eggs with white, brown or even greenish shell colours. A lot of such shell, shape and colour abnormalities reflect an unbalanced diet,  stress, hen’s age or even sickness, but some  -especially the shell colours- are genetically fixed.

Cracking an egg open can give you the surprise of not only finding one, but two or even more yellow egg yolks, but finding no yellow at all may surprise you the most!  Such eggs are known as fart or wind eggs and were once thought to be those of roosters. In fact, it’s the very young or very old hens that are likely to produce yolkless eggs. On one occasion I found a complete little egg with its own shell inside another and, of course, much bigger egg with its own shell. Apparently, this can be caused by an egg reversing its course in the egg tube or oviduct and getting packaged into a newer egg. However, it’s not a big problem: when fresh, both are edible. Also edible, when fresh, are unsightly eggs that exhibit blood patches near or in the yolk. The blood stems from vessels that carry yolk-building material to a hen’s ovary.

There are in rare cases chicken egg abnormalities that I myself during the time we kept chickens had thankfully never been confronted with. A nematode worm known as Ascaridia galli can occur in eggs laid by hens that suffer from a high parasite load. The twisted whitish bands in the egg white that are attached to the yolk and hold it in place are a normal component of eggs and must not be confused with such worms. Certainly more worrying are microbes like Mycoplasma synoviae (which alter the shell surface, cause thinning and increased shell translucency) and Salmonella enteritidis. The latter can enter damaged eggs or may even occur in clean, intact shelled eggs as a result of infections of the reproductive tissue of laying hens. However, it doesn’t show up as an egg abnormality and you won’t notice it until you start vomiting, develop a fever, stomachache, and diarrhoea. But then it’s too late and you had better decide – if you feel like eating an egg again-  to purchase your next carton of eggs from a different supplier who only sells fresh eggs kept not above 20℃ (Salmonella loves temperatures around 30℃).


© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content. 

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