EMBRY NIC DEVEL PMENT Day 0
The embryonic disc looks like a ring: it has a brighter central zone where the embryo is located.
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Narrowing of the neck. The brain progressively penetrates the cephalic region. Formation of the beak. The embryo begins to adopt a bird-like shape: wings, legs and beak are clearly visible.
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The vitelline membrane almost covers the entire yolk. Pigmentation of the eye is clearly visible and upper and lower components of the beak are observable. Aperture of the external auditory canal. From this moment on, the phosphorus is used for skeletal formation.
START OF BLOOD CIRCULATION
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The germinal disc is in blastoderm stage. With its development on the surface of the yolk, it also begins the development of a membrane that later on will envelop the yolk: the vitelline sac.
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In the first two days the embryo is very sensitive due to the fragility of the blastoderm and the formation of the vascular network (towards 40 hours of life).
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Clearly visible “diamond” - shaped beak and nostrils present as a narrow openings. Extension of the distal portion of the extremities; the lower parts are covered with feather follicles.
Growth of allantois and increased vitelline vascularization. The vitelline sac envelops the yolk, and thus nutrient absorption intensifies. Nails appear and the beak is able to open.
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The embryo rests on its left side. The trunk, head and brain can be distinguished. The vitelline membrane extends over the surface of the yolk. The heart structures are already visible and begin to beat. Blood circulation starts.
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Development of the amniotic cavity. It surrounds the embryo and is filled with amniotic fluid that protects the embryo and allows its mobility. The allantoic sac appears. This structure plays an important role in respiration, calcium absorption and waste storage.
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Feathers begin to appear. The allantois is fully developed (internally lining the entire eggshell) and functional, while the vitelline component begins to decrease.
The digits of the feet are completely formed. Nails and beak acquire consistency, and the diamond is clearly visible. Metabolic production of heat and the need to eliminate it increases.
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Appreciable increase in embryo size, with the adoption of a C-form shape. Extension of the extremities, with differentiation of the digits on the hind limbs. Eye pigmentation begins.
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Important lung growth. The eye is almost completely closed. Allantois decreases in size and transforms into chorioallantoic membrane. Embryo uses protein of the egg white. Marked increase in calcium mobilization from the eggshell.
START OF PULMONARY RESPIRATION
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Kidneys become functional. Intestinal digestion and absorption begin at around day 15-16. Allantoic sac begins to accumulate excretions from embryonic kidney. The reduction in vitelline component accelerates and the albumen has almost completely disappeared.
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Embryo is completely covered in down and positioned parallel to the long axis of the egg with the head oriented the right, in preparation of eclosion. The air chamber is quite large.
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Head is positioned between legs and the head located below the right wing with the beak pointing towards air chamber. Egg white is completely reabsorbed and renal system produces urates.
The yolk or vitellus begins to penetrate the abdominal cavity, and the amount of amniotic fluid decreases. This is the time (18-19 days) to transfer the eggs from the incubator to the hatching unites.
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The head of the embryo is positioned below the right wing and beak points toward the air cell. Yolk absorption accelerates and the amniotic fluid disappears. Large proportion of chicks pecks the air chamber starting gas exchange through lungs.
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The yolk sac is located within the abdominal cavity, this still unhealed navel. Pulmonary breathing becomes fully implemented and blood flow in allantois decreases. The chick perforates the internal membrane of the shell and breathes in the air chamber.
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The chick uses its wing as a guide and its legs to turn on itself, and breaks the shell in a circular manner using “diamond”. It causes an important increase in oxygen consumption.
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The vitelline membrane continues to grow and surrounds more than half of the yolk. Amniotic component decreases in size. Voluntary movements begin. Proventriculus and gizzard are formed, and the liver begins to differentiate.
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The eye is closed and the down almost covers the entire body. The embryo begins to rotate and gradually becomes positioned parallel to the long axis of the egg, turning the head towards the obtuse pole.