TERMINOLOGY

When reading the Breed Standard for any breed, it will give specific descriptions of the important areas for each breed, variety and gender – if there are differences between them. Some varieties will be the same for both sexes and noted as such (for example, solid coloured birds).

 

THE MAJOR EXTERNAL PARTS OF A CHICKEN:

To be able to work with chickens, a breeder must know the various parts of a chicken and their functions, and know the difference between male and female chickens.

Beak – The chicken’s beak serves three functions. First, it is the chicken’s mouth. Second, it is used for fighting and protection. And third, it functions as the teeth of the chicken, enabling the bird to break grass, fruit and other foods into pieces small enough to swallow.

Comb and wattles – It is believed that the comb and wattles of chickens serve to cool their blood.

Ear lobes – The ear lobes of chickens serve hearing and other ear functions.

Eyes – The eyeball of a chicken is stationary; thus, a chicken must move its head to vary the range of vision.

Feathers – Feathers provide insulation and buffer extremes of heat and cold.

Wings – Chickens cannot fly very well. They can flap their wings sufficiently to raise themselves about three meters (3m) off the ground.

Tail and tail feathers – The tail is used for balance while walking and, in flying, as a rudder for up – and – down and side – to – side motion.

Feet and nails – In addition to walking, feet and claws are used in fighting (for protection) and in finding food.

 

DIFFERENCES BETWEEN MALE AND FEMALE CHICKENS THAT SHOULD HELP IN IDENTIFICATION:

Size – The male will grow taller and usually weighs between 0.5 kg and 1 kg more than females of the same age upon reaching maturity. A male of one breed may weigh less than the female of another breed. This greater size is not apparent until the chicken attains four weeks of age. At one day old there is no difference at all between male and female chicks.

Comb and spurs – The comb and wattles of the male will become much larger than the comb and wattles of a female. On the female, spurs hardly develop at all when compared to the male.

Vocal expressions – Everyone knows that a rooster crows while a hen doesn’t. What is not generally known is that rooster’s crow intermittently all day long, not just in the morning.

Feathers – Adult males have distinguishably different feathers from those of adult females. The most distinguishable are the tail feathers which are long and stringy on the male. Hackle and neck feathers of males have pointed ends, whereas those of females have rounder ends. In addition, males have sickle feathers in their tails and hackle feathers on their backs which and females do not have.

 

THE EXTERNAL ANATOMY OF A CHICKEN:

 

 

 

 

 

SKELETON

All animals have a skeleton to protect their internal organs and tissue and allow them to stand up straight. The avian skeletal system looks similar to those of their mammalian counterparts, but there are some important differences. Many of these differences relate to the bird’s need to be light enough to fly while still maintaining the needed body support.

Some important differences between the skeletons of birds and mammals are listed below:

1. Some of vertebral sections are fused together to provide the rigidity required for flight.
2. The Sternum provides a large surface area for the strong attachment of the main flight muscles.
3. The size of the head has been reduced significantly when compared to other species. A large head would make flying more difficult.
4. The tail has been reduced to a very short section of fused bones called the pygostyle (sometimes referred to as the Parson’s nose or the Pope’s nose).
5. The ribs have been modified by the inclusion of the uncinate process which refers to overlying flaps projecting off the ribs connecting ribs to the ones beside them. This gives strength to the rib cage so that it won’t collapse during flight.
6. The neck is quite long in most species to enable the bird to protect the delicate tissues of the brain from too much jarring when landing – the flexibility of the neck acts as a shock absorber.
7. The chicken bones are lighter because some bones in the body have air sacs. Some other bones, like those in the skull have spaces inside.
8. Another difference between chicken and mammal bones is that chicken bones have more minerals. Some of the minerals that chicken bones are rich with are calcium and phosphate. Mammal bones contain those minerals as well, but not as much as in chickens.

 

THE INTERNAL ANATOMY OF A CHICKEN:

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CHICKEN BONES

Like most other bird varieties, chickens have a light skeleton, consisting of hollow bones. Fortunately broken bones are, very rare in chickens, for these hollow bones rarely heal.

 

SKULL

The skull of the chicken consists of many small bones and the face is made up of the nasal and the premaxillary bone. The largest bones in a chickens face are called frontal-, parietal- and temporal bones. They make up the cranium which is the back of the chicken head. There is also a jaw bone which is called a mandible.

 

BREAST

One of the largest bones is the breast bone or sternum. It is so large that it covers more than half of the body cavity. The sternum has a carina, which is a large kneel.  Carina is used to attach the wings so that the bird can fly. Chickens are not good flyers and usually can fly only a very short distance. This is why their carina is not as large as in the flying birds. The breast bone is attached to the ribs.  Chicken have five or six pairs of ribs and these bones protect the organs inside. A chicken’s shape is very much determined by its breast bone. Depending on the breed, the breast muscles are either normally or highly developed. The build can be correspondingly either broader or more delicate. Also the breastbone’s length varies from breed to breed. For example, the typical build of the Old English Game Bantam is the result of a short breastbone.

 

BACKBONE

Chickens are vertebrates. Vertebrates are animals that have a backbone. The chicken backbone starts with the atlas. This is the small bone on top of the spine. This bone is important because it allows chickens to move their heads.  Chickens usually have about 20 vertebrae, but this depends on the breed. The spine ends with a cervical bone.

 

THE WISHBONE

The wish bone is the slingshot looking bone and is sometimes pulled apart and a person who gets a larger part makes a wish. The wishbone is actually a clavical or collar bone. It connects the shoulders of a chicken. It also makes an opening so that digestive and respiratory tract can pass into the chickens body.

 

NECK

The neck aid in the reaching of food located on the ground. The rigid body would make this simple activity more difficult without the modification aid of the adjustment of the centre of gravity which is needed when the bird changes from the upright position of walking or perching or to the more horizontal position of flight. The bones of birds are also lighter in weight than those of their mammalian counterparts. A chicken has fourteen neck vertebra that are small and highly flexible. Chickens can turn their heads 180 degrees and they are also able to move it vertically and horizontally.

 

PNEUMATIC BONES

Some of the bones are hollow and actually act as part of the avian respiratory system. They are called pneumatic bones (pronounced New-Matic) and include the skull, humerus, clavicle, keel (sternum), pelvic girdle, and the lumbar and sacral vertebrate.

 

MEDULLARY BONES.

Another important type of bone in the avian skeleton is medullary (pronounced Med-U-Larry) bones. These include the tibia, femur, pubic bone, ribs, ulna, toes and scapula. Medullary bones are an important source of calcium when hens are laying eggs. Egg shells are primarily made of calcium and a hen mobilizes 47% of her body calcium to make an egg shell. When in production, a commercial-type laying hen cannot obtain enough dietary calcium for daily egg production. Without medullary bone to draw calcium from, the egg shells would be very thin and weak.

 

DIGESTIVE SYSTEM

Chickens do not have stomachs like other animals, but have a different means of food storage and digestion. First the food enters the beak (mouth) and goes halfway down the esophagus (throat) to a storage area called a crop where it is moistened and thus softened. Food then continues down the remainder of the esophagus and enters what is called the proventriculous, or true stomach. The proventriculous secretes digestive juices (enzymes and acids), and is directly attached to the gizzard which grinds food up into smaller pieces. Food leaving the gizzard enters the small intestine where nutrients are picked up by blood vessels and circulated throughout the chicken’s body. Food particles then move into the large intestine, which has two “blind” or dead end attachments called ceca. (The functions of the ceca are not understood fully.) After digestion in both intestines, the waste materials including both urine and stools are excreted through one opening called the vent. The excreted material is called faeces.

 

THE HEART AND LUNGS

The heart and lungs of a chicken function in the same way as these of most other animals. Air enters through the nostrils then goes down a tube called the trachea, located right beside the esophagus. Both tubes are located on the underside of the neck when the chicken is standing. The entrance point to this air tube is located at the back of the beak and is called the larynx. The trachea looks like a thin plastic tube with rings around it. This ends at a Y-shaped junction and two bronchial tubes lead off to the right and left lungs. The trachea and bronchial tubes look like semi-transparent plastic tubes. The lungs are segmented and located between the rib bones leading from either side of the back bones of the chicken. Going further back towards the tail, you find the reproductive system, then, closest to the tail, there are pockets in a larger bone which contain the kidneys. If normal, the kidneys are brownish red in colour.

The first thing visible in an opened slaughtered chicken while lying on its back is the liver which is divided into two parts. The liver is just in front of the soft skin above the vent. There is often yellow or white fat between the skin and the liver. The normal liver is the same or slightly lighter colour than the typical animal liver found in the marketplace. Under and in front of the liver is a small sac of green fluid called the gall bladder. Under the liver and the intestines above the kidneys, is a small ball-shaped organ called the spleen. The spleen is lighter in colour than the kidneys.

 

REPRODUCTIVE SYSTEM

If the female adult chicken is laying eggs a mass of egg yolks ranging in size from microscopic to almost 3cm in size would be found at the rear of the lungs and along the back the ovary. The smaller ones will be opaque. Egg yolks enter a tube through what is called the funnel. The funnel leads to the oviduct through which the yolk passes and in which the egg white, then the shell, is formed, a process which takes about 24 hours. Upon mating with a rooster, sperm passes through the oviduct system in the opposite direction. Fertilization takes place at the ovary end. Sperm may stay viable for up to 4 weeks and are stored in the oviduct.

 

THE CROP

You can feel the crop on the chest of the bird more down to one side. It is a sack-like extension of the oesophagus. It is a muscular organ that has some small pebbles collected by the hen to help make slurry of the food she eats. Water is added and the food is ground. This process takes longer if the animal has been fed wheat or corn instead of pellets.

 

THE STOMACH

Absorption of sugars, the beginnings of protein digestion, all take place in the stomach or proventriculus. Digestive enzymes are secreted into the stomach where the first stage of chemical breakdown occurs. Water is absorbed in the stomach and some amino acids, but the majority of the food absorption takes place in the intestines.

 

SMALL INTESTINE

The duodenum acts as the entry for the bile duct from the liver and the pancreas. Both organs have much the same function as in humans. Bile emulsifies fats as well as being a waste product from the liver. The pancreas provides a cocktail of enzymes that acts directly on food and also provides insulin that moderates chicken metabolism.

 

LARGE INTESTINE

This part of the chicken’s anatomy is punctuated by two blind sacs called caeca. In a way these are similar to the human appendix, mostly on account of their apparent lack of use. I dare say they will be found to have some use in the hen, even if it is a place of incubation of the bacteria that populate the rest of the lower gut. The large intestine is packed with bacteria that break down cellulose and the whole length of this part of the intestine reabsorbs water. Disease with this part of the animal brings with it the danger of dehydration.

 

CLOACA

This is the sewer of the hen, and the word ‘cloaca’ literally means sewer. It is a common space which both the oviduct and the intestine empty into, but in such a way that the eggs are not contaminated by the bird’s waste. As the egg is pushed out of the ovary and along its duct its presence pushes closed to the large intestine and the cloaca becomes all oviduct. When the egg is not there, the chicken’s own waste forces the oviduct portion of the cloaca shut, thus making it impossible for waste materials to enter the ovaries or their ducts. The final part of the digestive system is called the vent, which might refer to as the animal’s bottom. It is a sphincter, which means it is made as a closable muscle.

 

THE CIRCULATORY SYSTEM

All birds have almost identical circulatory systems as in humans. They have the same, four-chambered heart, which completely separates oxygenated and deoxygenated blood, essentially two circulatory systems with a single pump working them together. The chicken’s heart is very efficient and consists of two atria at the top and two ventricles at the bottom. The system of arteries and veins is largely the same.

 

 LIVER

Of course these wonderful little organs, actually the largest in the hen’s body, are so very tasty. Where would we be without pate? However, the liver is a very important organ for the living bird too, being the ‘chemical factory’ that metabolises most of the important substances a bird needs. The waste product of all this is called bile, which has a function in digestion.

 

KIDNEYS

Hens do have kidneys, even though they don’t have a bladder. They drain into an area in the cloaca called the urodeum. Uric acid forms in the liver and is removed from the blood by the kidneys and this is vented out in the cloaca via the vent.

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1. Shoulder butt or scapulars

2. Wing bow coverts

3. Lower wing covert

4. Secondaries

5. Wing bow coverts

6. Axial feather

7. Flight coverts

8. Primaries (ten in number)

9. Tertiaries (Mainly waterfowls

 

 

 

 

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