Lucas Delgado
The chick embryo undergoes several developmental stages before hatching from its egg, which typically takes 21 days. Before the egg is laid, the embryo begins to develop, but this process pauses until favourable conditions are met, either under a broody hen or in a controlled incubator. Once conditions are suitable, the embryo resumes development, absorbing vital nutrients from the eggshell. During this time, the embryo's cells differentiate, forming the nervous system, feathers, beak, claws, skin, respiratory and digestive systems, skeleton, muscles, circulatory system, and more. By the fourth day of incubation, the embryo has all the organs necessary to sustain life after hatching, and by the seventh day, digits appear on the wings and feet, with feathers and feather tracts visible by day 10. After 21 days, the chick begins its escape from the shell, using its egg tooth and neck muscles to cut the shell and emerge.
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What You'll Learn
Embryonic development begins before the egg is laid
The development of a chick embryo begins even before the hen lays the egg. Once the egg is laid, development pauses until favourable conditions are met, either under a broody hen or in a controlled incubator.
The embryonic development of a chick begins when a sperm cell fertilises a female egg cell, forming a zygote. About five hours after fertilisation, the zygote enters the isthmus, where the embryo starts to develop by simple cell division. By the time the egg leaves the isthmus, the zygote, now called the blastoderm or embryo, comprises eight cells, and after four hours in the uterus, it has grown to 256 cells. Initially, the dividing cells form one layer over the yolk, but as cell division continues, two layers are formed: the ectoderm (uppermost) and the endoderm (underneath) layers. Soon after, a third layer of cells called the mesoderm, or middle layer, is formed. The organs and tissues of the bird will develop from these three layers of cells. The ectoderm produces the nervous system, parts of the eyes, feathers, beak, claws, and skin. The endoderm produces the respiratory system, the digestive system, and secretory organs. The mesoderm produces the skeleton, muscles, circulatory system, reproductive organs, and excretory system.
By the time the egg is laid, the embryo consists of many cells differentiating into various tissues, organs, and body systems. Once the egg is laid, some embryonic development has occurred, and it usually stops until proper cell environmental conditions are established for incubation to resume. At this stage, all the cells are alike, but as the embryo develops, cell differences are observed. Some cells may become vital organs, while others become a wing or leg.
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. Torsion and flexion continue through 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.
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Incubation stage
The transformation of an egg into a chick is one of nature's miracles. The incubation stage of chick embryo development is a complex process that usually takes 21 days, sometimes 22 days, of favourable conditions for the chicken to develop and hatch. During this time, the embryo undergoes rapid growth and development, transforming from a single cell into a fully formed chick.
On the first day of incubation, the first signs of resemblance to a chick embryo emerge. Within 20 hours, the vertebral column appears, followed by the nervous system, and then the beginnings of the head and eye. On the second day, the heart begins to form and blood islands begin to link, creating a vascular system. By the 44th hour, the heart and vascular systems join, and the heart starts beating.
By the end of the third day, the beak begins to develop, and limb buds for the wings and legs are visible. On the fourth day, the chick embryo's body turns 90 degrees, and the head and tail come close together, forming a "C" shape. The mouth, tongue, and nasal pits develop as the digestive and respiratory systems take shape.
The embryo continues to grow and develop rapidly. By the seventh day, digits appear on the wings and feet, and the heart is enclosed within the thoracic cavity. After the tenth day, feathers and feather tracts are visible, and the beak hardens. On day 14, the claws begin to form, and the embryo moves into position for hatching.
During the incubation stage, the embryo relies on the egg for its nutritional requirements, except for oxygen. It develops special membranes to access nutrients in the egg and carry out essential bodily functions. The temperature must be carefully controlled within a narrow range of 37-38°C for optimal development.
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Organs and tissues develop from three layers of cells
The development of a chick embryo is a complex process that takes around 21 to 22 days, including one day in the oviduct and the remaining time in an incubator or nest. The transformation of an egg into a chick is considered one of nature's greatest miracles. Initially, all the cells are alike, but as the embryo develops, they begin to differentiate. Some cells may become vital organs, while others develop into specific body parts like wings or legs.
During the early stages of development, the dividing cells form two layers: the ectoderm (uppermost) and the endoderm (underneath). These layers cover the yolk, providing a foundation for the embryo's growth. However, soon after the formation of these initial layers, a third layer of cells, known as the mesoderm or middle layer, emerges. This marks a significant step, as the organs and tissues of the bird will develop from these three layers of cells.
The ectoderm plays a crucial role in forming the nervous system, parts of the eyes, feathers, beak, claws, and skin. It contributes to the sensory and external features of the chick. On the other hand, the endoderm is responsible for the respiratory system, the digestive system, and secretory organs. This layer lays the groundwork for the chick's internal functions and processes.
The mesoderm, nestled between the other two layers, gives rise to the skeleton, muscles, circulatory system, reproductive organs, and excretory system. This layer is instrumental in shaping the structural and reproductive aspects of the bird's anatomy. The development of these three layers is a dynamic process, with cells changing and adapting to produce different types of cells required for various tissues and organs.
By the time the egg is laid, the embryo consists of numerous cells that are differentiating and organizing themselves into distinct tissues, organs, and body systems. The embryo's development continues, and by the end of the fourth day of incubation, it possesses all the necessary organs to sustain life after hatching. The chick embryo's rapid transformation from a collection of cells to a fully formed creature is a testament to the intricate and fascinating process of chick embryo development.
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Chick breaks out of shell
The process by which a chick breaks out of its shell is known as hatching, and it marks the culmination of the chick's embryonic development. This development begins even before the egg is laid, but it pauses once the egg is laid and resumes only when favourable conditions are met, either under a broody hen or in a controlled incubator. The ideal temperature for optimum development is 37-38°C.
After the egg is laid, the embryo continues to develop rapidly. By the end of the fourth day of incubation, the embryo has all the organs it needs to sustain life after hatching, and most of its parts can be identified. On the seventh day, digits appear on the wings and feet, and the heart is completely enclosed in the thoracic cavity. 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.
By day 21, the chick is in the hatching position, the beak has pierced the air cell, and pulmonary respiration has begun. The chick uses its egg tooth—a sharp, horny structure on its upper beak—and the muscle on the back of its neck to cut through the shell. It rests and changes position, cutting until its head falls free of the shell. It then kicks free of the bottom portion of the shell. The chick rests while its navel openings heal and its down dries. Gradually, it regains its strength and walks.
After hatching, baby chicks appear drenched and feeble, but they rapidly become lively. They start shedding their soft down and sprouting new primary feathers. It takes a chick about 18 weeks to become an adult.
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Post-hatching, baby chicks appear drenched and feeble but grow rapidly
The transformation of an egg into a chick is one of nature's greatest miracles. After hatching, baby chicks appear drenched and feeble, but they rapidly become lively. The yolk that a chick absorbs before hatching sustains it for 2-3 days post-hatching. During this time, the chick is dependent on the mother hen to find food.
The first year of a chick's life consists of four stages: incubation and hatching, baby chicks, pullets, and adult hens. Each stage has its own challenges and requirements. For example, baby chicks require diligent care, including regulated temperatures starting at 95°F during the first week of their lives. They are susceptible to diseases like coccidiosis as they are still developing their immune health. A brooder, or a home for newly hatched eggs, is essential for those without a mother hen. It provides a dry environment with adequate ventilation and fresh bedding, promoting the baby chicks' immune health and keeping diseases at bay.
During the incubation stage, the baby chick absorbs vital nutrients from the eggshell. The development of the chick embryo pauses once the egg is laid and resumes when favourable conditions are met, either under a broody hen or in a controlled incubator. The ideal temperature for optimum development is 37-38°C. Fluctuating temperatures above/below 20°C weaken the embryo.
The embryonic development of a chick begins when the sperm cell fertilises the female egg cell, forming a zygote. About five hours after fertilisation, the zygote enters the isthmus, where it develops into an embryo through cell division. By the time the egg leaves the isthmus, the zygote has grown to 256 cells. Initially, the dividing cells form one layer over the yolk, but as cell division continues, two layers are formed: the ectoderm (uppermost) and the endoderm (underneath) layers. A third layer of cells, the mesoderm or middle layer, is soon formed, and the organs and tissues of the bird develop from these three layers.
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Frequently asked questions
The first stage of development for a chick embryo is fertilisation, when a sperm cell joins a female egg cell to form a zygote.
During the first few days of incubation, the embryo develops vital organs, including the heart, which begins beating by the end of the third day.
Throughout the rest of the incubation period, the embryo develops feathers, claws, and other key features. By the tenth day, feathers and feather tracts are visible, and by the fourteenth day, the chick is moving into position for hatching.
During hatching, the chick uses its egg tooth and neck muscles to cut through the shell. After emerging, the chick rests while its navel openings heal and its down dries.
After hatching, the chick will shed its soft down and grow new primary feathers. It will also start to develop bones and lay eggs.
