The Science and Anatomy of an egg

Most people see it as a simple oval form, we eat it for brekfast, poached, boiled, scrambled or fried, to us it seems like an everyday thing, but an egg is more than that. It is a fascinating structure, and also contains the potential of life.
An egg is protected by a porus shell made up of calcite, a christalline form of calcium carbonate. It is semipermeable, meaning water and air can pass through via the thousands of tiny pores. The egg has a very outermost layer called the cuticle which protects ftom bacteria. On the inside of the shell there are two membranes. The inner and the outer membranes are surprisingly tough. They are made up partly of keratin, which is found in hair, skin and nails, and act as a bacteria barrier.
When the egg is freshly laid it is warm, but once it cools the contents shrink, leaving an air space between the two membranes. The air space grows larger as the egg ages, which is why incubated eggs have large air gaps when shone through with a candling lamp.
Inside these two membranes there is the albumen or egg white which is made up of water and many different liquid proteins. The ‘chalazae’ are twisted ‘ropes’ of protein holding the yolk and also acting as shock absorbers. This structure can be seen on a fertilized, unincubated egg. The viteline membrane encases and supports the yolk.
The yolk contains protein, fat, water (to a lesser extent) and vitamins and minerals. This is where the chick obtains nutrition. The yolk ranges from pale yellow to deep golden depending on breed and management. Chickens that roam freely and eat lots of green generally have golden egg colour.
The eggs colour ranges from white to dark brown, with green and blue hues as well. The pigment is the last thing that is added during its formation in the ovary and depends on breeding and genetics.
When the egg is laid it comes out of the vent. Both eggs and droppings share this opening but the set up and placing of various organs inside the hen ensures that the two never come in contact. There is also no urinary opening to complicate matters, a chickens urine is not liquid, it is the white part of the droppings, called urates. The sunshine that a plant absorbs makes it green, while the sunshine that the hen eats when she eats the plant makes her eggs yolk yellow. Battery eggs are have pale yolks, because the only sunshine the hen gets is that that her food contains.
The meat spot is a small deposit of blood sometimes found in the yolk. It gives no indiction that the egg is fertile, it is simply caused by the rupture of a bood vessel during the eggs formation. It is safe to eat but can be removed before cooking with the tip of a kife.
Occasionally a hen may lay an egg that has no yolk or a double yolk, this is the result of an unsynchronyzed production cycle an usually occurs at the begining or end of the laying period. A double yolked egg should not be used for breeding so if the egg is extra large don’t be tempted to use it.

Even when she is young, a hen has more egg cells than she will ever lay. These are rudimentary or germ cells. The egg ripens and a yolk forms around it in layers. It travels down the oviduct, and at this point would recieve sperm from the male. The chalazae are formed and a membrane covers the yolk.  Then, liquid protein called the albumen, or egg white is added in layers, the last one being firm and spongy as a shock absorber. Then, the shell is formed and in the last three hours pigment is added. During incubation the chalazae break, so the hen turns the egg occasionally to keep it centred.

I hope this article has expanded your knowledge, if you are interested in more science subjects, take a look at our The science behind a chickens eyes page and our chicken genetics page.

Chicken Breeding- An Introductory Guide to Breeding Chickens

 

Artificial Hatching

Breeding Flocks

Broodiness

Fertilization

Hatching Without a cockerel

Natural Hatching

Recognizing broodiness

Summary

 

 

Breeding flocks

Whether for home breeding or commercial purposes, if you want your chickens to have chicks you need to choose a good, healthy breeding flock. This involves selecting quality birds, which must be healthy, and must also conform to their breed standard.
You should choose birds that are 100% healthy. Their feathers should be shiny and smooth and they should have clear eyes and nostrils.
The maximum number of hens you can have with one cock depends on the breed. With big placid breeds like Brahmas you can normally keep two to five hens with one cock, while with a light, slender, very active cock you can keep up to ten or even twelve hens!

Chickens must be healthy, and conform to their breed standard before you can even THINK about adding them to your Breeding Flocks.

Fertilization
All hens that are to be used for breeding should be at least one year old as when they are one year of age they reach full maturity and have generally got better hatching and laying rates. Even if they are laying before this age, making them go through the stressfull process of raising chicks may have detrimental effects on their development if they are not yet fully developed.
If your cock becomes infertile, don’t worry, as infertility whether in old or young is normally temporary. It could be that he is too fat and therefore not in good breeding condition. Also, it could have something to do with the time of year. Some cocks are active all year round and others only in the breeding season. If, however, he is infertile for more than a couple of months, especially if he is old, it may be time to consider a new cock.
Mating in chickens is called treading. An active cock is one who mates his hens a lot; a non-active cock is one who doesn’t mate them at all. To tread a hen the cock mounts her and grips her neck feathers. To pass sperm from cock to hen they join sex openings and the hen can then receives the sperm. Many eggs can be fertilized by just one treading, as it is possible for the sperm to stay alive for more than ten days.

Frequently trodden hens often have bare patches on their neck and back where he has ripped her feathers out due to his vigorous activities. This can be remedied by moving the cock to a seperate run for a while, or adding more hens to his flock.
Hatching Eggs
Egg hatching can be done with a broody hen or with an incubator. The latter is an option for mass production, or for people who dont have a broody, while the former is natural and is done by people who keep hens as a hobby.

Artificial Hatching

Some incubators only need water added to keep the embryos moist as they automatically turn the eggs, regulate the temperature and do everything else for you, whereas the more basic incubators require you  to turn the eggs and set temperature yourself. It is helpful to mark the eggs with a cross on one side and a circle on the other so that you know which side to tun them onto.
Eggs should be turned over the pointed end three times a day so that the embryos don’t stick to the shell. This should be done to all eggs that are intended for hatching, even if they are just being stored in boxes. It is best to place the eggs with the tip pointing inwards. Once the eggs have been put in leave the incubator lid on all the time unless you are turning the eggs. In many incubators, there will be two water compartments in the middle. Fill one of them up but leave the other. In others, there may be only one. Fill this up part of the way, as instructed (in instruction manual).

Eight days into the incubation period it is useful to find out if the eggs are fertilized.You can find out using a candling lamp, a specialist lamp that you can buy either from incubator specialists or an animal feeds merchant. Candling lamps should be used in a very dark spot, otherwise you cant see anything! Hold the lamp against the egg. If you see a dark spot that moves away from the light, you’ve got a live embryo. Sometimes all you see is a dark spot but other times you see a maze of blood vessels. If you see a spot of blood it could either be a dead embryo or an infertile egg (in which case the spot of blood is probably the ‘meat spot’ which is caused by the rupture of a blood vessel during the eggs formation in the hen.) All infertile (clear) or dead (blood ring, blood spot, dark ‘thing’ sticking to the shell*,) eggs should be disposed of (best on the compost where they will be broken down).

*There is an exception to this. sometimes these can be live embryos, the dark thing being the vitelline membrane ( full of veins and arteries), which resembles the placenta in humans. If this is the case you will see a dark spot move away from the light within the dark ”thing”.

Two days before the chicks are due, stop moving the eggs and fill the second compartment with water to aid hatching. This will cause more humidity to build up in the incubator. This is essential for the chicks to pip.
Be patient, as hatching can take as long as two days, so if they are a day too early or too late don’t worry!
There are two membranes in an egg, one inside the shell and the other around the chick.
When hatching, the chick rolls around and takes the yolk sacks and blood vessels inside it. If a chick is having difficulties, some people help them while others are strongly against it, for they say if the chick is weak it should be left to destiny. If you think any of your chicks are weak do not try to help them out by cracking the shell in any place because if they have not done their rolling antics, it makes it all even harder, if not impossible!

For twenty-four hours after hatching chicks can live without food. This does not mean that you should not give them food, once they are dry and in a box they should have access to food!!! It is best to leave the chicks in the incubator until they are totally dry.
Your chicks may start lying around in strange positions because they need to rest and they don’t know immediately how to lie properly. Once they are totally dry, carefully put them into a box with shallow sawdust, a very shallow bowl of water and a shallow rimmed food tray. They should have an infra red lamp and a shelter under the lamp where they can get warmth and shade.
Eventually, with time the chicks will get the hang of standing, grooming and lying down!
Broodiness
Having a broody hen has many advantages over artificial hatching. Whereas, among other things, a hen can teach her chicks how to survive an incubator is just a humming machine. The temperature in an incubator can fluctuate or there could be a powercut, ending the embryos life. Despite this incubators have their own advantages, chicks can be hatched without a broody hen and through lots of handling, the chicks also become much tamer.

Breeding Without a cockerel:

Believe it or not, this can be done. You need a broody hen, suitable housing, time and patience, but not a cockerel! How does this work? You buy hatching eggs! These should be bought from a reputable breeder. They shoukd also NOT be purchased online, and certainly NOT from eBay. You should ensure the eggs are not older than 7 days, and dont get them ent through the post! Even if they all come through in one piece, they will have taken a battering during transport, from which they will never recover, regardless of the amount of ”Fragile. Handle with care” notices the box is adorned with!!!
How to recognise Broodiness

  • A broody hen sits on the nest for long periods of time sometimes refusing to leave it.
  • Being aggressive to other hens or her handler.
  • Certain parts of the abdomen and breast become featherless (‘brood patches’).
  • She makes ‘clucking’ noises.
  • She puffs herself up when anyone or anything approaches

Natural Hatching
Using a broody hen to hatch eggs is an easy option, for all you have to do is wait (and of course, tend to the hen).
It is best to separate a broody hen from the rest as otherwise other hens will come and lay more and more eggs and they will get mixed up and your hen will sit on far too many eggs, which will all be due for different dates, so when her first chicks hatch, there will be lots more half brooded eggs!
Keeping two or more broodies in the same cage is no good either as they may start steal each other’s eggs and chicks!!!

Broody hens should have access to food and water at all times. It is ideal to keep them in an ”ark” house, that is low to the ground, so that they can have access to a bit of leg stretching space, and room for the chicks to explore without getting mixed up with the other chickens.

SUMMARY!

  • Only breed from healthy birds
  • If you have not got a cockerel, but do have a broody hen, you can buy hatching eggs.
  • Always read your incubator manual if you choose to use one
  • Broody hen are the most natural way to raise chicks
  • A broody must have food and water at all times!
  • Goodluck, and have fun!

And lastly, have fun with your chickens, whether it is to breed, for eggs or for exhibition!!!

Why not take a look at our other chicken care pages, they are loaded with information that you will need and treasure when you keep your own birds!