Gas exchange of the embryo facilitate this, an egg has about 10,000 pores, protected by the cuticle, a protective layer around the egg. This layer has no visible openings but gases can permeate through it. The cuticle is 0.010-0.005 mm thick. An egg that weighs 70 grams has the same number of pores as an egg weighing 60 grams, although the eggshell is thinner. The ratio between the content and the surface area of a large egg is relatively larger. For this reason, certainly with larger eggs, the gas exchange must not be restricted too much. This also means that a larger egg has more difficulty releasing heat, increasing the risk of overheating. On around day 11, calcium starts to be absorbed from the eggshell. The shell becomes thinner at this stage which improves the gas exchange.
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The exchange of gas takes place through the outer chorioallantoic membrane and the allantois. Oxygen (O2) supply is vital for the development of the chick, as is sufficient removal of carbon dioxide (CO2) and water (H2O). The exchange of gas with the outside world is similar to what happens in the placenta with the mother’s blood.
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An embryo in a hatching egg shares some similarities with a baby in the womb. Both need warmth and the exchange of gases. The main difference is that the egg already contains the nutrients for the embryo while a human embryo receives its nutrition via the placenta. An embryo needs sufficient oxygen (O2) for proper development. O2 is absorbed from the air through the pores in the eggshell. As the embryo continues to develop and becomes larger, it absorbs more and more O2 and produces waste products in the form of water (H2O), carbon dioxide (CO2) and heat. An egg should be porous enough to allow the chick to breathe, but at the same time large losses of moisture should be prevented. No bacteria should be able penetrate the egg either. To
Incubating too warm is like running a marathon During a marathon, rapidly available energy from carbohydrates is used first. The body then switches to burning fat. Burning fat requires a lot of oxygen. If you keep running too fast, your body will start to utilise proteins from the heart muscle and the immune system. If you maintain a calm pace, you won’t experience any problems. The link with embryonic development? A hatching egg has a carbohydrate supply for the first week. After this, the blood vessel system has developed sufficiently to be able to transport oxygen and therefore burn fat. As the temperature of the embryo increases, the metabolism increases and, with it, the oxygen demand. If insufficient oxygen is absorbed, the system switches to burning protein. In this way, (locally) incubating too hot affects the heart and the immune system. The availability of oxygen plays a key role. This is determined by the presence of oxygen in the air, but also by the eggshell quality and the breed of chick.
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Carbohydrates
Fat
Carbohydrates
O2
Fat
Carbohydrates
O2
Fat
O2
Protein (heart, immune system)
Ha tc he ry S i gnal s
