A chickens Brain- The Science

Did you know that chickens have a concept of the future?

Scientist used tho think that only humans and higher primates had brains with structure that is complex enough to allow forethought. The complex arrangement of the neurons, and the  fact that they have a concept of the future suggests that they are intelligent enough to worry. An example of this is shown when a strange person comes to the breeders house, puts them in a box and into a roaring creature with legs that go round and round (a car!!). They dont peck around happily, instead they make noises of alarm and worry what is going to happen to them. An even worse scenario is when they are stuffed into crates, loaded onto a lorry and brought to a slaughterhouse.  This is a terrible state for them to travel in, and they spend their time worrying what will happen to them.

The neocortex is the part of the brain that deals with complex thought. Chickens have one of these too.

An egg can only hold up to 200 calories, and many calories are needed for a big brain. This is why mammals go through the pain of childbirth, because they give their young a constant supply of calories, and their young grow a big brain. Despite possessing a tiny brain (about the size of a pea!!), chickens fit a lot into it. Their spinal chord, and some parts of the brain deals with movement, co-ordination and reflex, while the rest of the brain deals with memory, senses, future conceps and voluntary actions. This is quite a lot to fit into such a tiny brain!

Chicken genetics

Inside every living cell, there is a nucleus (plural nuclei). This is the cells powerhouse, it controls the actions of the cell. Nestled in the cytoplasm among mitochondria and glycogen granules, the chromosomes are found within the nucleus. These structures, which become clearly visible under a microscope before they split, otherwise rest as chromatin granuals. These control the organisms characteristics by means of genes. Lined up on every chromosomes are genes which control egg colour, eye colour and other traits. Chickens have 78 chromosomes, some being sex chromosomes (so called due to determining gender and sex linked characteristics) micro and some being macro chromosomes.

Cells divide by meiosis and mitosis. Mitosis is where the chromosomes replicate and line vertically up the middle. The chromosome and its replica are called chromatids. They cross over each other in the centre and are held together by centromere. The cell splits vertically and the daughter cells have the same amount of chromosomes as the first. Mitosis is used for growth in plants and animals and asexual reproduction in plants.

In meiosis the chromosomes replicate and line up in two vertical lines in the centre of the cell. One row moves right, the other left and the cell splits down the middle. The chromosomes arrange themselves across the middle of the daughter cell. The chromatids seperate and travel to opposite ends of the cell, and the cell divides again. After the dividing has finished, the result is four cells, each with half the original number of chromosomes. Meiosis is used for sexual reproduction, so that when the egg is fertilized, the chromosomes in the males sperm complete the set of chromosomes. If this didnt happen, then the number of chromosomes each individual posesses would double with every generation.

A cell with the full number of cells is diploid, while one formed by meiosis is always haploid.

The gender of the individual is determined by certain kinds of chromosomes and their genes. In  humans, females are homogametic, meaning that the two letters that represent their gene type are the same but  with chickens the cockerel is homogametic. A ZZ chromosome is male, while a ZW chromosome is female.

Sex linked traits are carried in one copy on non-homogametic genes, while the homogametic gene carries two copies. As the male carries the larger amount of copies, he is mostly responsible for traits such as egg colour in his chicks.

Principles; Basic poultry genetics

These are just some basics that are essential for hobby breeders, covering basic DNA and genes.

1) There are two strands of DNA, twisted into a double helix. At each ‘point’ in the DNA that we call genes, the gene is equal on both sides. This means that there can be one or two doses of the gene. One dose is known as heterozygous, two are known as homozygous.

2) The ‘ locus’ is a name given to the point where the gene  falls on the DNA. Sometimes, several related genes are found on the same locus, these are known as allelles. If there are two different genes on the same locus,  this is called a heterozygote. A homozygote is where two doses of one gene are found on the same locus (one on each strand).

3) ‘Sex linked’ is a term used to describe a gene found on the z-chromosome. The z chromosome from hens only affects her sons and is known as sex-linkage.

4) If there is one dose of dominant gene it will make an effect on the phenotype ( The way genes act and the effect they produce). One dose of recessive gene makes them a ‘carrier’ for the gene, but its effect is not displayed.

5) A multi-interaction gene is where several genes are needed to produce an effect. A good example is the gene for single lacing. Pg, Co and Ml are needed for the plumage to show that marking.

This is useful information, especially if you plan to breed or study avian genetics. I hope you found this feature interesting and educative.

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.

The science behind a chicken’s eyes

Recent scientific discoveries have shown that chickens eye sight is better than that of mammals (humans included) in terms of colour. A chickens retina (light sensitive structure) is organized in a complicated structure of interwoven mosaics, and the cones (colour sensitive) can detect colour spectrum that human’s cannot. While humans can detect red, green and blue wavelengths, most birds (chickens included) have receptors for red, blue, green, violet and ultraviolet meaning that they may see an entirely different dimension.. Where a human would see green dots, a chicken would see different coloured dots, depending on the varying amounts of ultraviolet light.
When light enters the eye through the pupil which expands and contracts to allow sufficient light through, it travels through the lens and is reflected at the retina .The chickens retina can detect not only detect some ultraviolet wavelengths but also has special motion sensors which allow them to see motion in a way that we do not truly understand.
If a chickens eye is viewed side on, you will see that they have a transparent ‘bulge’. This is called the cornea. Did you know that chickens have eyelids? Three infact. They have a nictitating membrane, which is between the other eyelids. It slides sideways over the cornea and cleans and protects the cornea with lubricating fluid from a duct that serves the same purpose as our tears. their bottom eyelid moves up to meet the top one when they close their eyes, but they only close these eyelids when they are sleeping.

If you like science subjects, why not look at our Chicken genetics page and our The Science and Anatomy of an egg page, or browse our The Science of Chickens category.

Egg Laying in Chickens


Even as a chick a hen has all the eggs she will ever lay in her ovaries, in an immature form called  rudimentary egg cells (yolks- to- be ).
How quickly this supply is used up depends on breed, feeding, housing and hygiene.
If you use an artificial light to keep your hens laying through the winter their store of rudimentary cells will be used up faster. In her first year, a hen lays the largest amount of eggs that she will ever lay in one year, although the total weight of the eggs she lays stays roughly in her first and second year because in her second year, although the individual number decreases, the size of the eggs increases.

The size of the hen barely affects that of her egg. Take Wyandottes and Dutch
bantams for an example. In the picture the egg above is that of a Wyandotte
while the one below is from a Dutch bantam and Wyandottes are many times
the size of a Dutch bantam.

Colour also varies greatly from white to dark brown with beige, cream, blueish,
Greenish and pinkish at various ends of the spectrum!
In the formation of the egg the pigment is added last.
A yolk is released from the ovary and the albumen (egg white) forms around it, covered with a membrane.
The egg rotates through the body, giving it its form and then the shell is formed.
Last but not least the pigment is added.

There is a time in the year when hens will take a break from laying. Some people switch to cheeper  food because  the hens arent laying, but that is the wrong thing to do. By taking a break, the hens are recharging their batteries, so if anything, they should be fed better food!

You must have an adequate nestbox, or the hens will go and find their own place to lay, sometimes in a bush, or in a hedge or, more frustratingly, under the shed! Nestboxes should have a ‘lip’ at the front to stop the litter spilling out. They should be about 30cm wide and 40cm long. they should have 40cm walls to give the hen privacy, because, hens like quiet, peaceful, dark places to lay.

If you collect eggs daily, your hens shouldn’t get a chance to taste an egg but if they do they will probably start pecking open freshly laid eggs. A dark nestbox helps to prevent this behavior. Once they acquire this habit they are unlikely to stop unless you interfere, you can (most of the time) stop this behaviour by making a hole in an egg, spilling its contents on the nest box floor and adding non-toxic foul tasting liquid like mustard and chilli pepper.

Reduce stress, dont have bright lights around the nestbox. Chickens may also eat eggs because they are not getting enough calcium, so it is worth providing a calcium supplement, in liquid form to add to water, or as oyster shell grit. If this doesn’t work you can make a double bottomed nest box with sloping floor where the egg rolls down a crack to the bottom floor where soft material breaks its fall, so that it is out of the chickens reach.

To find out more about eggs and their anatomy and science click here.