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Does chicken egg shape determine chick sex?

Chicken egg shapesPerhaps you've heard the old wive's tale that you can determine the eventual sex of a chick by looking at the shape of the egg?  A quick search of the internet will turn up testimonials from dozens of chicken-keepers who are absolutely certain that this method of sexing chicks works.  Here's one representative sample from Chicken Keeping Secrets:

“My answer is yes you can tell the sex of an egg before it is even placed in an incubator. Several years ago I was told that the more pointed eggs would be roosters and the more rounded eggs would be hens. So I decided to do an experiment. I set 24 eggs in an incubator and hatched 20 of those eggs and they were all roosters except one. I currently try to use only the more rounded eggs for hatching and have about 75 % hens. This does not appear to be true for all breeds of chickens but does seem to work for the large breeds but not as well on bantams.” ~  Thanks, Donald R. Holbrook

I decided to dig a little deeper, and stumbled across this line from The History of Animals by Aristotle:

"Long and pointed eggs are female; those that are round, or more rounded at the narrow end, are male."

It looks like the tale goes back to the fourth century BC...although egg shape had the opposite meaning back then.  Does that make it an old philosopher's tale?

Despite what Aristotle thought, modern scientists poo-poo the notion that egg shape is an indicator of chick sex.  After all, if egg shape had any effect on sex, wouldn't hatcheries incubate all female eggs rather than risking public outrage by euthanizing unwanted males?  The scientific literature suggests that egg shape is breed specific, inherited from the hen's father, and may vary seasonally.  So don't choose only round eggs to put in your incubator and assume you won't end up with a rooster --- chances are that 50% of those eggs will hatch into males.

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I can't see the exact statement made, so I'm quoting as a similar phrase; "after all wouldn't commercial hatcheries use this". The technology for using this method is patented.

http://www.patentstorm.us/patents/7167579/claims.html The patent expires in 2022.

Additionally, I struggle with generalizations such as; scientists don't validate this. What scientists? What published research based study did the scientist use to make this determination?

Comment by tbeck late Tuesday night, February 22nd, 2012

tbeck --- Thanks for sharing! Unfortunately, just because something has been patented, doesn't mean it works...

Just thinking through the biology, it would be hard to see how egg shape could be linked to the sex of the chick. Since the mother hen makes the egg shells around the embryo, she would somehow have to know the sex of her offspring, which seems highly unlikely.

Comment by anna at lunch time on Wednesday, February 22nd, 2012

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