CHAPTER 9:
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Hatching
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In the last two and a half days before hatching, a lot happens in the chick’s body. It absorbs more oxygen, because its lungs are activated and it begins pipping into the air cell. The chick begins using
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its lungs for respiration, and the blood circulation through the chorioallantoic membrane (CAM) is shut
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off (the membranes dry out). This causes the metabolic rate to increase. The chick produces more heat. Then it begins pipping the eggshell, and a healthy chick will see the light of day.
In natural conditions, the hen occasionally stands up around hatching: alternating fresh air and warmth. The CO2 concentration in the hatcher is initially 3,000/4,000 ppm (outdoor air = 400 ppm). At the time of pipping, around day 19, the CO2 concentration can even rise to 8,500 ppm, depending on the air inlet position. At around 20 days, ventilation is used to reduce this to 3,000 ppm at hatch. 132
If all goes well, more than 90% of the transferred eggs hatch and you will have healthy chicks. If the eggs were not incubated under the right conditions or the gas exchange was sub-optimal, the embryos will have been unable to convert all the yolk and albumen optimally into growth and development. These embryos will be smaller and there will be more yolk residue. In order to survive they have taken more energy from their livers, hearts, and muscles, and will feel as if they have just run a marathon... They are exhausted, and it is questionable whether they have enough energy to hatch from the egg. The yolk has not been retracted well, and these chicks often have poorly sealed navels.
Ha tc he ry S i gnal s
