Ventilation is important in incubators 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.

Egg shells 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 4th or 5th day of development another structure, called the "allantois," grows from the embryo, extends through the albumen, and positions itself just underneath the egg shell. The allantois becomes the primary respiratory organ of the developing embryo and remains such 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 egg shell.

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.

So how should you set the dampers (air inlet and outlet regulators) in your incubator? Since there are so many different makes and models, it would be too difficult to attempt to recommend a procedure for each one. Instead, here are some general guidelines for proper ventilation:

  • The air exhausted from a hatcher or incubator should be vented (ducted) to the outside of the building. This is especially true if the incubator is located in a closed building or a small room. Such a venting system, if properly installed, provides added assurance that fresh air is available to the developing embryos. Nearly all of the large commercial poultry hatcheries are set up with this type of venting system. Small, home-type incubators are usually not designed for easy installation of vent ducts and, therefore, are seldom used. Instead, one may find four or five incubators operating in a 10'x12' room, exhaust air spilling into the room, and intake air being pulled in from the same room. Sometimes all the windows and doors will be closed to, as the owner says, "help hold the heat and humidity up in the incubator." Restricting the room ventilatior may help with temperature and humidity control, but ventilation suffers. In such an instance, the incubators are only able to circulate the stale, expelled air back through the machine that the embryos reuse for respiration. Recirculating stale exhaust air through the incubators can be reduced by placing the incubator in a large room with a few openings, or in a small room with a number of large openings (windows or doors). The best way is to either duct the used exhaust air outside and provide enough openings for fresh air to enter the room, or to provide plenty of openings for fresh air to enter and stale exhaust air to easily escape.

  • The largest amount of air exchange is needed toward the end of the incubation period because the embryos are larger and respiring more.

  • On large commercial incubators the dampers are always in the motion by slowly opening or closing unless they reach the point of being fully open or closed. Temperature inside the incubator regulates the opening and closing motion. If the thermostat is set on 100oF., the dampers begin to open when the temperature is above 100oF., and begin to close when the temperature is below 100oF. (The dampers are set so they never completely close.) With this method of control, the dampers tend to remain near the closed position during the winter months when colder air is being brought into the incubator. Conversely, during the late spring, summer, and early fall months, the warmer intake air usually causes the dampers to stay about half to full open. This same pattern fluctuates on a day-to-day basis in the spring by cool nights and hot days. During early embryonic development less heat is given off by the embryo and, therefore, the dampers tend to close more than they would be with embryos in the latter stages of development. The summary explanation for manual damper setting in single stage incubators is as follows:

    1. Provide more ventilation as the embryos grow larger and as the outside temperature increases.

    2. Provide approximately the same total size intake and exhaust openings (some incubators have one intake and two or more exhaust openings).

    3. Give as much attention to proper ventilation as you do to temperature, humidity, etc.

    4. Provide a way to get rid of the exhaust air, especially in small closed type incubator rooms, so that the machines can take in fresh clean air.

    If multiple egg settings are made in the incubator, causing the embryos to be in various stages of development, environmental changes have the greatest influence on the need for damper change. Unless the intake air is quite cool, the damper openings should not be set more than one-half closed if the machine is almost full of eggs.

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