Commercial Poultry Production and Hatchery Management

VENTILATION

• Ventilation is important in setters and hatchers because fresh oxygenated air is needed for the respiration (oxygen intake and carbon dioxide given off) of developing embryos from egg setting until chick removal from the incubator.
• The oxygen needs are small during the first few days compared to the latter stages of development.
• Eggshells contain three to six thousand small holes, called "pores", through which oxygen passes from the air to the developing embryo and through which carbon dioxide passes from the embryo to the outside air. The embryo's lungs are not developed during early embryonic development to the point that they can accommodate respiration by breathing.
• Respiration, therefore, is provided during the first three to five days by the vitelline blood circulation plexus growing from the embryo.
• To reach this plexus the gaseous exchange must travel through the egg pores and the albumen (egg white) to reach the vitelline circulation, which lies on the surface of the egg yolk.
• After the 4^th or 5^th day of development another structure, called the "allantois," grows from the embryo, extends through the albumen, and positions itself just underneath the eggshell. The allantois becomes the primary respiratory organ of the developing embryo until just before pipping begins.
• The transfer of respiratory function from the allantois to the lungs begins three or four days before pipping.
• The transfer is gradual and is completed by the time the chick finishes pipping the eggshell.
• The important thing to remember about embryonic respiration is that ventilation is important throughout the incubation process, especially toward the end, because the embryos are larger and respiring at a much higher rate than in the beginning.
• The oxygen content of the air at sea level is about 21%. For each 1% drop in oxygen level below 21% decreases hatchability by 5%.
• The main danger of decrease in oxygen level by increasing the level of CO₂ that is toxic to the developing embryo.
• The tolerance level of CO₂ in the setter is 0.5%, whereas in hatcher it is 0.75%.
• When the level of CO₂ goes beyond 1.0% hatchability is reduced to a significant level and completely lethal at 5.0%.