External pipping
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The chick uses its egg tooth to pierce the eggshell.
The head of this chick seems to look strange with a kind of hump on the back of the head. But this is very normal. The strongly developed neck muscle is the so-called pipping muscle. After hatching, its size decreases again.
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After internal pipping, it takes approximately 3-6 hours before the chick breaks the eggshell (= external pipping). The hatchery manager must not attempt to force this process. During the transition to oxygen uptake through the lungs (lung respiration), the yolk is entirely retracted into the abdominal cavity and the navel seals. The chick rests for a half day after external pipping. The chick starts tapping the shell to enlarge the hole an hour before hatching. At a certain moment, the chick has to turn itself a little, to be able to make the hole large enough. The chick must turn around completely to be able to completely ‘unzip’ the eggshell. The RH must not be too low at this stage, otherwise turning will be difficult and the chick may stick to the eggshell membranes. After hatching, the chick dries off while taking a rest again (3-6 hours, depending on conditions). Some hatchers automatically detect the beginning of the hatch window, based on the increase in RH (humidity peak starts), and start the corresponding program step. You can see the dried chorioallantoic blood vessels in the eggshells and sometimes albumen residue.
The pipping line usually runs counterclockwise (as seen from above).
The chick pips the egg along a diagonal line, until the egg is 80% open. After this, it opens the eggshell section like a lid.
The hatching process Time before hatch 26-24 hours What happens? • Pipping into the air cell. • Oxygen uptake through the lungs (respiration) activates. • A mucus layer is applied to the inner side of the lungs, to protect them from dehydration.
9. H at c h i n g
Time before hatch 24-15 hours What happens? • O2 decreases. • CO2 increases. • The chick experiences a shortage of oxygen.
Time before hatch 15-12 hours What happens? • The chick pips the eggshell with its egg tooth. • Oxygen uptake now fully through the lungs (respiration). • The yolk is completely retracted into the abdominal cavity. • The navel seals.
Time before hatch 12-0 hours What happens? • The chick starts pipping the eggshell again with its egg tooth. • It enlarges the opening by turning around. • The chick begins to kick with its feet.
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