Thursday, April 7, 2016

Two Chicks in One Egg

Yesterday I was wondering if a fertilized double-yolk egg would contain two baby chicks.  Today when I was searching YouTube for a video for the previous post I stumbled upon the two videos in the first story below.  

Sometimes the Internet scares me.  I didn't speak to anyone about my musings on twin chick, nor did I address the Internet for answers on the subject.  But This morning I was presented with a two-part video on the subject while looking at a video about the finding of a rare Shakespeare volume.  Go figure...

Twin Yolks & Twin Chooks?   
From fowl lovin' to omelette, Dr Karl takes us on the journey of the humble egg, and answers the breakfast brainteaser. Can a double yolker can give rise to twin chickens?  By Karl S. Kruszelnicki

We humans eat hundreds of billions of chicken eggs each year. In the course of handling eggs over thousands of years, we have noticed odd things about eggs - such as how they don't have to have just one yolk. And so people have wondered - can an egg with two yolks give rise to two baby chickens?
Folklore says that an egg with no yolk at all is unlucky, because it was laid by a cockerel. A double-yolked egg is also supposed to be unlucky, because it implies an imminent death in your family. But a fertilised double-yolked egg...?

So to work out what's going on, we need to understand what happens to a follicle (or "pre-egg") after it's made in the ovary. It goes through five regions of the oviduct, on its way to the outside world, as it gradually turns into the egg that we love so much. 

The first region is the funnel of the oviduct, the infundibulum. This muscular section "catches" the egg as it leaves the ovary. In laying hens, it's about 7.4 cm long. The egg spends about 20 minutes here. The infundibulum feels a little like cling wrap plastic. This is where the sperm lurk having been left there by some rampant rooster, and where fertilisation may occur. By the way, rooster sperm can survive for 30 days in the infundibulum. The longest that human sperm can survive in a friendly environment is only three or four days. 

The second region is the "regular" oviduct, the magnum. It's the longest section, at 32.5 cm long, and holds the egg for about 3 hours. The magnum is a glandular region. Here, two layers of albumen are laid down around the central yolk. About half of all the albumen gets added in the magnum. The remaining half is supplied by the next two sections, the isthmus and the uterus.

The third region is the narrow part of the oviduct that leads into the uterus, the isthmus. The egg takes 70 minutes to get through this short section, only 8.7 cm long. Here, water is added to the albumen, and the inner and outer shell membranes are deposited. These membranes are made from complicated fibrous proteins. The air space that you see in eggs is between these inner and outer membranes. As the egg gets older, it loses water through the pores - so the air space gets bigger.

The uterus, or "shell gland", is the fourth region of the oviduct. Even though this section is only 8.3 cm long, the egg spends about 19 hours here. The hard calcium shell is added. The hard shell provides strength, but is also porous enough to allow just the right amount of water loss and gas exchange.
The last region of the oviduct is the vagina. It's the shortest of all, only 7 cm long.

Now the laying of the egg is very sophisticated. As the uterus pushes the egg outside the body, it virtually turns itself inside out - and then contracts itself back in again. As a result, the egg usually doesn't touch any faeces on the way out.

The egg finally leaves the hen via the "cloaca". This is a Latin word meaning "sewer". While female humans have separate external orifices for urine, faeces and copulation, female chooks have a single all-purpose orifice to the outside, the cloaca.

There are three main options of what can happen when a follicle is generated by the ovary of a chicken.
In the first option, everything goes normally and one day later, the chicken lays that egg, complete with shell.

In the second option, the yolk does not get picked up by the infundibulum. Instead, it ends up in the abdominal cavity, and is eventually reabsorbed. This happens from time to time in cockatiels. But as part of the process of the reabsorption of the egg, massive amounts of fat appear in the blood. As much as 30% of the volume of the blood is fat! This causes a process called "sludging", where the blood suddenly has large blobs of fat. These blobs can block the flow of blood to important parts of the brain. 

It's fairly common for the affected cockatiel to suffer a mild stroke. The characteristic sign is that they tilt their head over to one side. But magically, they somehow recover within a day from their mini-stroke - something that we humans cannot do.

The third option is that the ovary will generate two yolks at the same time. Unfortunately, they rarely hatch.

These two videos are about ten minutes each.  Extracting two chicks from the same egg is a delicate and slow process.  If you want to "cut to the chase," skip up to about 7:30 on the first video.  

In a sat-on-and-hatched-by-mum egg, the chicken has to rotate around, so it gets its head up to where the air cell is (the round bit). Then, under normal circumstances, the baby chicken will peck its way out.
But if there are two chickens inside, they will almost invariably fight each other. Neither of them will be able to get to the air cell, so they both die.

However, there have been a few very rare cases where the egg has been very carefully opened at exactly the right time (in a kind of mini-Caesarian), and two chickens have survived from a double-yolked egg.

Twin ducks hatch from one egg
Twin ducklings have hatched from the same egg at a duck farm in Cornwall. 

Romulus and Remus are the first recorded twin ducklings to ever hatch and survive in Britain Photo: SWNS
The Telegraph  26 Oct 2009

Roger Olver watched on as the chicks emerged to become the first recorded twin ducklings to ever hatch and survive in Britain. 

The ducklings - named Romulus and Remus - are to be spared the table and become pets at the Cornish Duck Company in St Austell, Cornwall. 

Mr Olver and partner Tanya Dalton had overseen the hatching of a group of eggs when they noticed that one was left uncracked. 

Miss Dalton decided to lend a hand and saw a beak peck through at one end, but she was stunned when seconds later another bird emerged from the other end. 

Mr Olver, 56, said: ''When we did the hatch there was one duckling left struggling to get out at the end.
''When a beak did stick through, Tanya tried to make the hole bigger to help it get out. But then she felt something else pecking her from the bottom of the egg. 

''It was unbelievable. Two ducklings from the same egg. We managed to get them both out and now they are doing fine. They are in perfect health. 

''They're looking pretty good, bearing in mind they were cooped up together in the same shell.'' 

MIss Dalton, 38, described the births as a ''miracle'' and has prepared an area at the farm where they can be kept as pets. 

She added: ''It was so exciting because you're told that it's impossible - that two could ever survive like this. 

''So when it happened, for two to come out alive and well, it was so special. It's a miracle really. 

''We decided we had to keep them, so they will have their own little run on the farm.'' 

The twins are the first of their kind to survive in Britain. A similar pair, hatched in Canada, did not survive. 

Roger and Tanya rear 300 ducks a week from their farm and sell to shops and restaurants across the country. 

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