General Chicken Information
Chickens are highly social animals that develop a pecking order or social
hierarchy. The rooster is the most dominant animal and the hens sort out their pecking
order based on size and aggression. Once the pecking order has been determined the
flock as a whole will do many activities together such as foraging, dust bathing and
preening. The foraging behavior remains strong even in large commercial operations
where the chickens are fed a very concentrated and nutritious diet. Their food
requirements are met in a very short period of time but they will still spend much of the
day pecking, probing and flicking with their beaks and scratching with their feet. A good
producer should allow this behavior to occur unimpeded.
Domestic chicks are very precocial when they hatch and will quickly learn to eat
and drink even without the aid of the mother hen. Most commercial operations either
hatch their own chicks or get them as day olds and they have few troubles as long as the
food and water are obvious. Maintaining the high body temperature is difficult for the
young chicks and they require a very high ( 32 C) environmental temperature to prevent
hypothermia from occurring.
Aggression towards people is usually restricted to the rooster who may fly at or
attach anything he preserves as a threat to his flock. Roosters may have spurs on their
feet that can inflict damage on intruders. Hens that are sitting on eggs to be hatched may
peck at anyone that tries to remove the eggs. Most times chickens will try to avoid
people and keep as much distance as possible between them.
Chickens have no lips, cheeks or teeth instead they have two horny growths on
the upper and lower mandible that is used to pick up food and is known as the beak. The
upper mandible is attached to the skull while the lower mandible is hinged to allow for
selectively picking up pieces of food. There is a dagger shaped tongue with a very rough
surface that helps to move the food into the esophagus.
Digestive System
Birds have developed a unique digestive system that helps to compensate for
having no teeth and therefore not being able to break down food particles in the mouth.
The crop is an extension of the esophagus before it enters the body cavity. It is basically
a storage pouch that allows the bird to quickly consume a meal and then let it digest
throughout the day.
Once the food leaves the crop it enters a structure that is truly unique to the birds,
known as the gizzard. The gizzard is made up of two very powerful muscles separated
by a very thick wall. When the gizzard is empty it remains inactive but as soon as food
arrives it goes into action. The food enters the gizzard and the two muscles start
contracting which will break the pieces of food into small particles. The gizzard will
usually contain abrasive material such as grit or gravel that helps to grind the food before
passing into the intestinal tract. The gizzard plays the role of the teeth in other animals
by breaking large pieces of food into small particles suitable for digestion. In wild or
free-range birds the gizzard is very effective at grinding up seeds and plant material but
in the commercial facilities the food passes through the gizzard very quickly.
The small intestine is the major site of nutrient absorption while the large intestine
is responsible for maintaining the water balance in the bird. The alimentary tract ends at
the cloaca, which means “common sewer.” The digestive, urinary and reproductive
tracts all empty into the cloaca. The urine of chickens is mostly uric acid and is seen as a
white pasty material that is evacuated with the feces from the cloaca.
Chickens have a fairly high body temperature (41.5 C) that in adult chickens is
maintained by a high metabolism and a good insulating layer of feathers. Feathers are
unique to birds and are composed of the same protein as scales, keratin. Birds are
thought to have evolved from the reptiles and they still retain reptile-like scales on their
legs and feet. Feathers do more than provide insulation, they also:
1) Aid in flight
2) Protect the bird from rain and snow
3) Provide camouflage from predators
4) Help attract the opposite sex of the same species
Day old chicks do not have feathers to help them conserve heat and great care
must be taken so that the young birds do not suffer from chilling. If the hen is present
when the chicks hatch she will crouch and allow the chicks to huddle against her
underneath her wings to share body warmth. This behavior demonstrated by the hen is
known as brooding. The time spent brooding the chicks is greatest during the first week
of life and slowly tapers off as the chicks get older. If the chicks are hatched out in an
incubator, ambient temperatures of 32 C should be present for the chicks during the first
week of life. The chicks’ behavior is the best indicator of proper temperature, chicks will
huddle together in a big pile if they are too cold and spread out away from the heat source
if too warm. As the chicks get older the temperature can be lowered until the bird is
fully feathered when the temperature can be maintained at about 18 C. Chickens have no
sweat glands and must rely on panting and vasodilation in the legs and comb to rid the
body of excess heat.
Chickens like all other birds are oviparous, their young develop outside of the
body in hard-shelled eggs that must be incubated. The incubation period for a chicken
egg is 21 days and when under a hen the eggs are turned regularly and kept at the
appropriate temperature and humidity. In a commercial incubator the egg is kept blunt
end up at 37.6 C and 60 % humidity for 19 days and rotated on a regular basis. The last
two days the egg is kept on its side at 37.2 C and 75 % humidity.
Once a hen is 20 weeks of age she will begin to lay eggs by continually releasing
ovum into the oviduct all year long. If semen is present the ovum is fertilized and an egg
will form which can then be incubated and produce a new chick. If no semen is present
the ovum is released and goes on the form an infertile egg that will not form a chick no
matter how long the egg is incubated (rotten eggs). Roosters are cued by the changing
daylight to begin mating with the hens. There is no physiological reason to breed the
hens it is just the roosters’ natural behavior to continually mate until the daylight hours
change again. Hens will crouch when approached by a rooster and copulation will occur.
The semen from the rooster enters the cloaca and then travels up the oviduct where it is
stored at semen storage sites until it is needed for fertilization. The stored semen can
fertilize ovum as they are released into the oviduct for 15 days but a hen is usually mated
again in that time. When group housed a single rooster can service up to 10 females and
ensure fertile eggs. Artificial insemination can be used in laboratory settings when the
background information such as disease status and vaccination program is needed for the
next generation. Turkeys are quite often artificially inseminated as the large tom is not
always able to mount the hen and if he does will quite often inflict injury.
In a commercial setting the chickens are kept at short day conditions (8 hours
light, 16 hours dark) until they are 20 weeks of age. They are then photo-stimulated by
changing the light pattern to 12 hours light and 12 hours dark. This change in light cycle
will induce the hens to lay and the roosters to breed As long as the light cycle remains
the same or the daylight hours increase the hens will continue to lay eggs and the rooster
will continue to breed.
Unlike mammals, in birds it is the female that will determine the sex of the
resulting embryo once mating has occurred. The rooster is homozygous and designated
ZZ while the female is heterozygous and designated ZW.
All birds grow and develop very quickly once they are hatched. Birds such as the
quail, chicken and ducks hatch young that are precocial or nidifugous. This means that
they are born with feathers and are capable of both locomotion and some degree of
thermoregulation soon after they are born. An altricial or nidicolous bird hatches out
young that are naked, unable to walk or thermoregulate. Examples of altricial birds
include hawks, eagles and pigeons.
Chickens have a high density of cone receptors in the retina suggesting that color
vision is important to the chicken. Newly hatched chicks have an unlearned preference
for the orange and violet colors that aid them in food detection while foraging. The
eyeball of the chicken is flatter than the mammalian eyeball and is capable of very little
movement. The field of view is 300 degrees for the chicken but is only capable of 26
degrees of binocular vision directly in front of the head. The chicken compensates for
this narrow range by having a very flexible neck and performing frequent head
Hearing is relatively good in chickens but is not an overly important sense for the
animal. The chicken has few vocal sound patterns for communication and relies mostly
on vision to detect predators. The sense of smell is very poor in the chicken and appears
to be relatively unimportant to behavior.
The chicken can distinguish between salt and bitter substances and will reject
solutions with even small amounts of these compounds. Chickens will avoid salty
solutions which makes it important to supply clean, fresh water at all times to ensure
optimal production performance. Taste sensitivities tend to be greater for liquids than
solids as most foods are swallowed whole and have little contact with the few taste buds
that are present on the tongue.
Commercial barns used for housing poultry have been designed to house large
numbers of animals and reduce the manual labor as much as possible. Most barns will
house many levels of chickens often stacked 3 or 4 layers high. Each cage is supplied
with an automatic watering system and an automatic feed delivery system that is often
computer controlled. If it is a layer barn there is a system of conveyor belts that will
bring the eggs to a central washing and packing area. The temperature, humidity and
lighting are often computer controlled or on automatic timers with a back up power
system in case of emergency.
Chickens can be either housed in cages or on the floor. Layers are usually kept in
cages and meat birds can be housed either in cages or on the floor. There are advantages
and disadvantages to both types of housing. The advantages of cages are:
1) Birds are separated from their feces, this provides a more sanitary
2) It is easier to observe and care for the birds, no birds are underfoot.
3) Eggs are cleaner.
4) Chickens in cages consume less feed.
5) Internal parasites and other diseases are lessened or eliminated.
6) More birds can be housed in a given space.
7) Labor requirements are reduced and working conditions are improved.
The disadvantages to using cages for housing are:
1) The investment per bird is usually higher.
2) The handling of manure can be difficult.
3) Flies can be more of a problem.
4) The bones of the caged hens are more fragile and easily broken.
5) Stress levels can be higher in the caged animals.
If space permits floor housing is often used to house meat producing birds. Day
old chicks can be housed in cardboard rings with a suitable bedding and an extra source
of heat (heat lamp or radiant heater). As the chicks get older the cardboard ring is taken
out and the chicks can have the run of the barn. The bedding used should be absorbent,
light, inexpensive and non-toxic. The bedding absorbs moisture and insulates the chicks
from the cooling effects of the floor as well as providing a cushion between the bird and
the floor. There are a number of types of bedding that can be used to house chickens
such as:
1) Wood shavings and sawdust
2) Crushed corn cobs
3) Chopped straw or hay
4) Recycled paper
5) Sand
When using the floor for housing the chickens it is common to use an all-in, allout type of management style. With this system a complete clean out of the manure and
disinfection of the barn will occur before a new batch of chickens is introduced. The new
chickens live and grow in the barn until they are shipped to market at which time the barn
is again completely cleaned and disinfected. The advantages of using this method of
housing are:
1) Disease organisms are much easier to remove when there are no living
animals present
2) No new birds are introduced into the established group, this reduces the
chance of introducing disease or causing behavior problems.
3) The uniformity of age within the group increases the immunity to disease.
4) Easier to clean and disinfect an empty barn, as well as maintain equipment.
No matter if the chickens are housed on the floor or in cages the other
environmental parameters to consider are the light cycle, temperature, and ventilation.
For the first 2 to 3 days of life chickens are exposed to 24 hours of light to ensure that
they find the water and feeding systems. The daylight hours will then become constant
until the producer wants them to start laying eggs. Temperature in a brooding barn
should be kept at 32 C for the first three days and then decreased as the chicken becomes
fully feathered. The chicken can then be maintained at a constant temperature that should
be kept between 18 –20 C. The ventilation system in the barn should be able to remove
the large amounts of dust, moisture and ammonia created by the chickens. The system
must also supply fresh, clean air at a low velocity so as not to cool the chickens. A
ventilation system should deliver 4-7 cubic meters of air per hour per kg of bodyweight
in the barn. There are a number of systems that will work but the main concern is to have
a backup system in place in case of emergency. High density housing of chickens
produce huge amounts of dust and ammonia and if they are not removed can quickly lead
to health problems or overheating.
Chickens housed in the lab will also have a number of options depending on what
type of trial is being conducted. In most cases the housing used in the lab should match
the style used in commercial operations. For example a food trial for broilers should be
conducted in as close to a commercial broiler environment as possible, probably floor
housing. If a layer bird trial is being conducted than a layer caging system should be
used in the lab setting. Cages may also be necessary if fecal collection is required for the
study. The environmental conditions should be easy to control in the lab and feed and
water systems should again match that of the commercial operations.
Poultry nutrition is a very complex, highly specialized business and there is
continual work going on trying to create the ultimate chicken diet. For producers a diet
that is inexpensive but still makes a chicken grow fast is ultimate goal. The high level of
research that has been done in poultry nutrition means that there are very good
commercial diets available for all types and ages of poultry.
Depending on what types of birds are being raised will determine what kind of
diet is to be fed. All chicks for the first 6 weeks of life require a high protein diet (19-23
%) that will allow for quick growth. After 6 weeks the layer chickens should receive 1618 % protein in the diet and the broilers should get 14-16 % protein. The layers require
the higher amounts of protein for the high energy requirements of egg laying. Protein
used in the diets will come from fishmeal, meat meal or vegetable proteins (soya bean).
Synthetic amino acids may be added to improve the quality of the diet if a poorer source
of protein is used.
The complete balanced rations can be fed as pellets, crumbs or a dry mash. The
crumbs are partially ground up pellets that are the right size to ensure that the newly
hatched chicks consume plenty of food. Pellets are fed to birds that need a high
consumption rate and are quick growers such as the broilers. A mash ration will be fed if
over-consumption is a concern, as the mash takes much longer for the chicken to
consume. Circular feed pans are often used to feed chickens as they provide a greater
feeder space than linear feeders. One circular pan 33 cm in diameter should provide
sufficient feeder space for 50 to 75 birds. If linear feeders are used 4.5 cm of trough
space per bird is required.
Water is perhaps the most important nutrient for an animal to consume, a chicken
can survive weeks without food but only a few days without water. Broiler chickens
during their lifetime (60 to 70 days) will consume 18 pounds of water and just 10 pounds
of feed. For a rough estimate the daily water consumption can be calculated by
multiplying the age the bird in days by 0.2 ounces. Daily water consumption is required
as the drinking water is often used to deliver medication, vaccines, vitamins and
Metal wing tags are the most popular means of individually identifying chickens.
The numbered tags can also come in different colors to help keep track of different
groups of chickens. The tags are clipped onto the wing web of the bird with a small pair
of specialized pliers. The wing web is a piece of skin that is formed between the wing tip
and the shoulder. The tag should not be placed into the muscle of the wing as this can
damage the bird. This is a very permanent and harmless means of identification if
properly attached.
Leg bands that are numbered and colored may also be used but there is much
more growth in the leg than the wing and may have to be removed to accommodate
growth of the leg. Non-toxic spray paint or wax crayons may be used to temporarily
mark birds.
Chickens have lots of good characteristics that make them suitable for use in
biomedical research:
1) Easy to house either on the floor or in cages
2) Small size makes them easy to handle and work with
3) Can be obtained as disease-free stock from suppliers
4) Genetically well defined
5) Produce an embryo that develops outside of the hen for all but the first 24
hours. Easy to monitor fetus development
A lot of the research work done with chickens concerns avian physiology or
pathology and has direct relevance to the health and management of domestic poultry. ,
Feed trials, vaccine studies, product testing and disease study are all done to improve
conditions and the welfare of meat and egg producing chickens.
The chick embryo provides a unique specimen to not only observe how a fetus
develops but also to see how immunity can be passed on through virus research. The
developing chick is also used to study all the disease causing agents, pharmacology,
nutrition, endocrinology and tissue transplantation. Vaccine production and diagnosis of
infectious diseases that can affect man are made possible by using cell culture techniques
using the chick embryo.
Although the chicken differs anatomically and physically from humans the
knowledge that we have gained from these birds is immense. Since 1929, ten Nobel
prizes have been awarded to investigators using chickens as the research subject. It is
thought that over 2% of all abstracts from most research journals have chickens as the
research subject. The importance of chickens as a research animal is immense and covers
all areas of investigation.
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