In article number 3 of this series by Jason Cormick, hatchery specialst at Petersime, we checked if your temperature regulation in the hatchery was still in great shape. Today we explain why the levels of CO2 should vary in line with the developmental stages the embryos are in.

Why and when should CO2 levels be raised or lowered

Gas exchange is of paramount importance for the embryo to survive. Oxygen (O₂), necessary to drive its metabolism, diffuses into the egg through pores in the shell and the produced metabolic carbon dioxide (CO₂) diffuses out of the egg along the reverse pathway. Gases are exchanged between embryo and the environment through the pores of the egg shell.

The level of O₂ is directly related to the level of CO₂. Control systems in incubators will monitor the level of CO₂ in the incubator rather than the O₂ level since it is easier to measure. Why does controlling the CO₂ levels during the entire incubation cycle have a beneficial effect on the development of the embryo and when should CO₂ levels become higher or lower?

Day 1 – 9: high CO₂ levels

As described earlier in this series “Optimize your value chain”, a mother hen will brood intensively during the first nine days of incubation, so ventilation around the eggs is low. As a consequence, oxygen levels are low and CO₂ in the nest is high. There is a very good reason for the hen to do exactly this, because limiting the amount of oxygen during the early embryonic stage leads to a better development of the chorioallantois (i.e. the vascular membrane), lungs and heart. Compare it to athletes: athletes from mountainous regions have an advantage over athletes living at sea level: they have a better lung capacity and a stronger heart because oxygen levels at high altitude are lower and their body develops to compensate this.

Day 10 – 17: low CO₂ levels

After these first nine days of incubation, the embryos require more oxygen to develop and they produce more CO₂. An enhanced chorioallantois permits the embryo to extract more oxygen through the egg shell at this stage. The hen will then leave the nest on an increasingly regular basis and go looking for food, allowing the embryos to take up more oxygen through their shell. Likewise, incubators also start ventilating more, giving the embryos access to more oxygen by lowering CO₂ levels.

Day 18 – 21: varying CO₂ levels

CO₂ levels can further impact the hatching process as it can delay or trigger internal and external pipping. Therefore, CO₂ levels can be adapted to accelerate or slow down certain phases in the hatching cycles, resulting in significant gains in hatch timing and chick uniformity. 

Boosting growth by controlling CO2 levels

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