Teaching The Life Cycle of a Chicken

Overview: The purpose of this lesson is to introduce the students to the stages in the lifecycle of a chicken.The students will learn how chickens progress from egg to chick, and observe eggs as they hatch.

During this Teaching the Life Cycle of a Chicken Unit Study, students will observe the fertilized chicken eggs, they will observe the incubation and hatching process, make predictions, and describe what they observe in their Life Cycle journals.

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Children will label egg diagrams, write a summary of the life cycle of a chicken and draw pictures for each stage, and draw and labele a sequence of events chart that shows the steps an egg goes through to hatch into a chick. Student will also observe the incubation and hatching process and describe what they see in their journals.

  • Incubator

  • Fertilized chicken eggs

  • Chicken embryo development chart

  • Magnifying lens

  • Journals.

To chickens, eggs are developing chambers for their chicks. Inside an egg is everything a developing chick needs until it hatches. A baby chick begins to grow at fertilization, when a sperm and an egg unite to form a zygote. Inside the hen’s body, the zygote begins to divide and form many cells. Meanwhile, it moves slowly through the reproductive organs of the hen. A day after the egg was fertilized, the egg is laid. At this time the embryo looks like a small white disk on top of the yolk.

During the three weeks the embryo is in the egg, it receives no food from the outside. Instead, its nutrients come from the protein and fat in the yolk. Water, vitamins, and minerals are supplied to the embryo by the albumen (the egg white). The chick also depends on the eggshell for the calcium necessary for bone formation. As the embryo removes calcium from the shell, the shell becomes thinner, allowing more oxygen and carbon dioxide to pass into and out of the egg.

Inside the egg, four embryonic membranes keep the embryo alive. The first membrane to appear is a sac around the embryo called the amnion (AM nee ahn). The amniotic fluid within the amnion is like the embryo’s private swimming pool. It cushions the developing chick and protects it from harmful chemicals. The next membrane, the yolk sac, surrounds the yolk. The allantois, another membrane, stores wastes and helps the chick exchange oxygen and carbon dioxide with the atmosphere.

During the first part of the embryo’s development, the area within the allantois takes up most of the egg. The outermost membrane, the chorion, lies just outside the albumen but inside the shell. Oxygen and carbon dioxide pass to and from the chick through the chorion. About 20 hours after the egg is laid and incubation has begun, the embryo still looks like a white disk floating on top of the yolk, but a streak shows where the spinal cord is beginning to form. At 33 hours, the primary brain regions, spinal cord, and heart have developed, and the embryo looks like a tiny rod on top of the yolk. During the next 15 hours, the embryo’s appearance changes drastically. Its body bends and twists until it lies on its left side, looking like a backward question mark. At this point the embryo basically consists of a brain, heart, and tail.

By the time the egg has been incubated two days, the embryo’s heart is beating in rhythm and many blood vessels that supply blood to the yolk sac and the allantois have developed. Blood passing the allantois picks up oxygen and gives off carbon dioxide and wastes. Blood returning from the yolk sac carries food to the embryo. The embryo’s eyes and ears are also forming.

By the third day small buds that will later become wings and legs are visible. A day later, most of the embryo’s organs have formed, but its head takes up almost half its body. In the remaining days, the body will grow much faster than the head. By the sixth day the embryo can move, its feathers are beginning to develop, and its bones will soon form.

Two to three days before the chick is ready to hatch, it grows a small egg tooth at the end of its beak. About the same time, the chick’s “hatching muscle” (located on the back of its neck) becomes swollen with fluids. Both these structures are necessary for the chick to break out of the shell.

Just before hatching, the chick breaks a hole through the egg’s inner shell membrane to the air space at the blunt end of the egg. The chick sticks its beak into the air space and for the first time uses its lungs. Loud clicking noises can be heard from inside the egg as the chick learns to breathe. Because this space holds so little air, the chick still depends on its allantois for most of its oxygen. But in a few hours, the chick pecks a hole through the shell and begins to breathe fresh air.

To begin the hatching process, the chick uses its hatching muscle to push its head upward and force its egg tooth through the shell. Then the chick pivots around inside the egg and makes a new hole. Eventually, the chick pecks a complete circle of holes in the eggshell. Using its head as a lever, the chick pushes on the cutout portion of the egg and struggles out of the shell. At first the chick looks very wet. But if you were to touch the chick, you would find that it is just moist. The feathers look wet because each is tightly folded and wrapped in a membrane. These membranes protected the feathers while the chick was in the egg and prevented them from taking up a lot of room.

When the membranes dry, they crumble, freeing the fluffy down feathers. The chick helps break these membranes by rubbing against its mother and other chicks. In an hour or two, the feathers are all free and the chick looks like a ball of fluff.

Lesson Introduction

What is an egg?

Where do eggs come from?

What does a bird have to do to hatch an egg?

What happens when an egg hatches?

What is a life cycle?

Exploring the Lifecycle Concept

Pass around an egg for the kiddos to examine. 

Use a magnifying lens to look at the shell, and have the kiddos describe what they see. One will see little holes in the shell. Ask what they think the holes are for, and explain that the shell is porous (has thousands of tiny holes), and that the embryo breathes through these holes.

Take a boiled egg and cut the egg open to show the different parts of the egg, and explain the function of each part. 

The yellow yolk is the food the growing chick embryo would eat.

The white/clear albumen provides additional food and water, as well as a protective cushion for the growing chick.

The hard shell also protects the chick embryo.

Have the kiddos make their own eggs with construction paper (yellow and white).

What is a mammal, and how is it different from an animal that lays eggs?

What are some other animals that lay eggs?

Identify and talk about egg-laying animals such as amphibians, reptiles, birds, fish, octopuses, snails, spiders, and insects.

The children will draw and label a sequence of events chart that shows the steps an egg goes through to hatch into a chick.

Development of the Egg: The Yolk:

The chicken egg starts as an egg yolk inside a hen. A yolk (called an oocyte at this point) is produced by the hen's ovary in a process called ovulation.

Growth of the Embryo: 

As the embryo grows, its primary food source is the yolk.  The exchange of oxygen and carbon dioxide gas occurs through the eggshell; the chorion lines the inside surface of the egg and is connected to the blood vessels of the embryo.

A chick emerges after a brief three weeks of incubation.

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On the second day of incubation, the blood islands begin linking and form a vascular system, while the heart is being formed elsewhere. By the 44th hour of incubation, the heart and vascular systems join, and the heart begins beating. Two distinct circulatory systems are established, an embryonic system for the embryo and a vitelline system extending into the egg.

At the end of the third day of incubation, the beak begins developing and limb buds for the wings and legs are seen.

On the fourth day, the chick's entire body turns 90 degrees and lies down with its left side on the yolk. The head and tail come close together so the embryo forms a "C" shape. The mouth, tongue, and nasal pits develop as parts of the digestive and respiratory systems. The heart continues to enlarge even though it has not been enclosed within the body. It is seen beating if the egg is opened carefully. The other internal organs continue to develop. By the end of the fourth day of incubation, the embryo has all organs needed to sustain life after hatching, and most of the embryo's parts can be identified. The chick embryo cannot, however, be distinguished from that of mammals.

Fifth day, the formation of reproductive organs and differentiation of sex.

Sixth day is the beginning of the beak.

The embryo grows and develops rapidly. By the seventh day, digits appear on the wings and feet, the heart is completely enclosed in the thoracic cavity, and the embryo looks more like a bird.

Eighth day, the chick is beginning to get feathers.

After the tenth day of incubation, feathers and feather tracts are visible, and the beak hardens.

On the fourteenth day, the claws are forming and the embryo is moving into position for hatching.

Sixteenth day, the scales, claws and beak becoming firm and horny.

Seventeenth day, the beak turns toward air cell.

On the nineteenth day the yolk sac begins to enter body cavity

After twenty days, the chick is in the hatching position, the beak has pierced the air cell, and pulmonary respiration has begun. The yolk sac completely drawn into body cavity; embryo occupies practically all the space within the egg except the air cell.

After 21 days of incubation, the chick finally begins its escape from the shell. The chick begins by pushing its beak through the air cell. The allantois, which has served as its lungs, begins to dry up as the chick uses its own lungs. The chick continues to push its head outward. The sharp horny structure on the upper beak (egg tooth) and the muscle on the back of the neck help cut the shell. The chick rests, changes position, and keeps cutting until its head falls free of the opened shell. It then kicks free of the bottom portion of the shell. The chick is exhausted and rests while the navel openings heal and its down dries. Gradually, it regains strength and walks. The incubation and hatching is complete. The horny cap will fall off the beak within days after the chick hatches.

When using an incubator, eggs must be turned regularly to prevent the yolk from settling to one side and to exercise the embryo. When you turn the egg, the embryo gets it exercise by turning in the shell until its head is upright. Eggs should be turned at least twice a day.  3 days before the eggs are to hatch, you should stop turning them.  The temperature should be kept at 100 degrees F.  In 21 days, you will have new chicks.

After 21 days, the chick hatches out of the egg. Chickens are precocial, which means they are born able to feed themselves almost immediately.The newly hatched chicks wander around and start to feed themselves by pecking at seeds, rocks, and insects. The chicks start to grow, and after a few weeks they are called a poults.

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