Normal Chicken Embryo
Development
About the Chicken
• The domestic chicken can be traced back to four
species of wild jungle fowl from Southeast Asia.
• Red jungle fowl is the most commonly found wild
species in the world today.
About the Chicken
• The rooster must be present for an egg to be fertilized.
• Most eggs that you buy at the supermarket are from hens
that are raised without a rooster being present.
• Roosters are not necessary at egg farms where eggs are
produced for consumption.
• Eggs for incubation are
grown at special farms
called breeder farms
where roosters are present
with the hens.
• No duh!
• Just making sure
Chicken Reproduction
• When a male chicken wants to mate with a hen, he will
do a little dance around her.
• Usually hens are not interested and just walk off.
• If a rooster feels like he just has to mate with a stubborn
hen, he will chase her down.
• If he is fast enough to catch her, he will grab on to some
feathers just below her comb and climb on.
• When the male bird is threading the hen he will grip her
back with his claws and her head with his beak.
• This behaviour continues typically only during the
breeding season (spring and early summer).
Chicken Reproduction
• Roosters do not have penises. They have a sperm glob
on their vent and will try to put it on the vent of the hen.
Sometimes it works sometimes it does not.
• For a higher rate of fertilization, a rooster should be with
no more then 6 hens together. As a rule, the more
aggressive the male birds are, the greater the chance
that their fertility levels will be high.
• The sperm live inside the female reproductive system
and each time an ovulation occurs (every 24-26 hours in
good egg producers) the egg can become fertile.
• This process continues and matings at 7 - 10 day
intervals are necessary to maintain fertility.
• After fertilization occurs the egg albumen, shell
membranes, and shell are added to complete the egg
formation process.
• The chicken usually lays the egg about 24 hours after
ovulation.
Chicken Egg Formation
• A hen requires about 24 to 26 hours to produce an egg.
Thirty minutes later, she starts all over again.
• The reproductive system of the hen consists of the
ovary, the organ where the yolk develops, and the
oviduct where the egg is completed.
• The ovary is attached to the back about halfway between
the neck and the tail.
• The oviduct, a tubelike organ approximately 26 inches
long, is loosely attached to the backbone between the
ovary and the tail.
• Most female animals have two functioning ovaries, but
the hen uses only one, the left. The right ovary and
oviduct remain dormant.
Chicken Egg Formation
• A female chick is born with a fully formed
ovary containing several thousand tiny
ova, or future yolks.
• These begin to develop, one at a time,
when the pullet reaches sexual maturity.
Each yolk is enclosed in its own sac or
follicle.
Chicken Egg Formation
• In this oviduct, all parts of the egg, except the yolk, are
formed. It is divided into five distinct regions: (1)
infundibulum or funnel, (2) magnum, (3) isthmus, (4)
uterus or shell gland, and (5) vagina.
• The infundibulum, also known as the funnel, captures
the ovulated yolk.
• This is where fertilization, if/when it occurs, takes place.
• After about 15 minutes, the yolk passes along to the
magnum.
• Here, in approximately 3 hours, the albumen is
deposited around the yolk
• As the albumen is formed, the yolk rotates, twisting the
albumenous fibers to form the chalazae.
Chicken Egg Formation
• The next site of activity is the isthmus where the
two shell membranes are formed in about 1 1/4
hours.
• The egg has now reached its full size and
shape, it passes along to the uterus to acquire,
after 19 hours, its shell, shell color and bloom.
• After a few minutes pause in the vagina, the
uterus inverts through the vagina, the cloaca
(the. junction of the digestive, urinary and
reproductive systems) and the vent to release
the egg outside the hen's body.
Chicken Egg Formation
• Laying of the egg is known as oviposition.
• During formation. the egg moves through
the oviduct small end first.
• Just before laying, it is rotated and laid
large end first.
• A young hen lays small eggs. The size
increases as she gets older
Chicken Egg Formation
Parts of the Egg
• You should be
able to identify
these parts on
a fertilized or
unfertilized egg.
• Which part is
not on the
unfertilized
egg?
•
•
•
•
•
The Shell
Looking at the egg from the outside we see the shell, which is a hard, protective
covering made of calcium carbonate. The shell is porous. (There are about 7,000
pores in a chicken eggshell.)
This allows the transfer of gases through the shell.
Carbon dioxide and moisture are given off through the pores and are replaced by
atmospheric gases, including oxygen.
Eggshell is made almost entirely of calcium carbonate (CaCO3) crystals.
The shell also has a thin outermost coating called the bloom or cuticle that helps
keep out bacteria and dust.
Parts of the Egg
• Immediately beneath the shell are two membranes, the outer and
inner shell membranes. These membranes protect the contents of
the egg from bacteria and prevent moisture from leaving the egg too
quickly..
• Because the body temperature of a hen is approximately 106° F,
eggs are very warm at the time they are laid. The temperature of the
air is usually much lower than 106° F, and the egg cools to the
temperature of its surroundings. As cooling takes place, the contents
of the egg contract more than does the shell of the egg. This creates
a vacuum and air is drawn through the pores of the egg.
• As a result, an air cell forms at the large end of the egg.
• While the embryo is growing, the shell membranes surround and
contain the white or albumen of the egg.
• The albumen provides the liquid medium in which the embryo
develops, and it also contains a large amount of the protein
necessary for proper development.
Parts of the Egg
• In a fresh egg, we can see white cords attached to the
yolk sac. These two cords, called chalazae, are made of
twisted strands of mucin fibers that are a special form of
protein. The chalazae hold the yolk in the center of the
egg.
• The yolk is the source of food for the embryo and
contains all the fat in the egg. The small white spot on
the yolk is call the germinal disc. The germinal disc is
where the female's genetic material is found.
When the egg is fertilized, sperm enter by way
of the germinal disc, travel to the center and a
chick embryo starts to form.
Extraembryonic Membranes
•
•
Protect and nourish the embryo
Terrestrial vertebrates have four
extraembryonic membranes
1.
2.
3.
4.
chorion
amnion
allantois
yolk sac
1. The chorion and amnion enclose the embryo
–
The chorion surrounds the entire embryo
•
–
in birds and reptiles it functions in gas exchange
The amnion encloses the embryo and forms an
open volume between the embryo & the amnion
called the amniotic cavity
•
The amniotic cavity fills with amniotic fluid, which envelops
the embryo and cushions it
2. The allantois is an outgrowth of the gut
•
In reptiles and birds, it stores nitrogenous wastes
3. The yolk sac encloses the yolk in vertebrates
with yolk-rich eggs
–
In humans, there is no yolk sac, but the yolk aids in
formation of red blood cells
Extraembryonic
Membranes
Primitive streak & groove
Credit: © Carolina Biological/Visuals Unlimited
Chicken embryo, 21 hours.
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heart
somites
Spinal chord
amnion
Credit: © Carolina Biological/Visuals Unlimited
Chicken embryo, 43 hours.
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eye
allantois
h
e
a
r
t
amnion
Spinal chord somites
Credit: © Carolina Biological/Visuals Unlimited
Chicken embryo, 60 hours.
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Credit: © Carolina Biological/Visuals Unlimited
Chicken embryo, 8 days.
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Credit: © Carolina Biological/Visuals Unlimited
Chick embryo, 9 days.
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Credit: © Carolina Biological/Visuals Unlimited
Chick embryo, 13 days.
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Credit: © Carolina Biological/Visuals Unlimited
Chick embryo, 16 days.
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Credit: © Carolina Biological/Visuals Unlimited
Chick embryo, 19 days.
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Credit: © Jerome Wexler/Visuals Unlimited
Newly hatched chick on day 21.
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More Resources
• http://www.ext.vt.edu/resources/4h/virtualf
arm/poultry/poultry_incubation.html