Normal Chicken Embryo Development. About the Chicken The domestic chicken can be traced back to four...

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.


• 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.


• 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.


• 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

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. chorion

2. amnion

3. allantois

4. 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



amnion

somites

heart

Spinal chord



eye

somitesSpinal chordamnion

allantoisheart

Chicken embryo, 8 days.


Chick embryo, 9 days.


More Resources

• http://www.ext.vt.edu/resources/4h/virtualfarm/poultry/poultry_incubation.html

Normal Chicken Embryo Development. About the Chicken The domestic chicken can be traced back to four...

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