Incubation Humidity and Ventilation

Humidity and Ventilation

A well-designed incubator should maintain temperature within 1/4 degree F and humidity within 1 degree F wet bulb temperature.

Short term variations in humidity are not important. The average humidity over the incubation period needs to be near optimum to achieve the ideal weight loss. High humidity for the day or two of hatching is also important. Beware chronic, excessive humidity.

Two factors affect incubation humidity: water evaporation within the cabinet (from eggs as well as from additional water) and levels of ventilation. The water content of the air being drawn through the incubator will also have an effect.   Monitor humidity levels and adjust to match published guidelines for different species.

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Important Incubation Procedures

For more specific information on particular species’ requirements check the relevant literature.

• Monitor egg weight loss which varies as a direct result of humidity and correct against published weight loss figures for the species.

Eggs lose moisture through their shells and the rate of evaporation depends on the humidity levels around the eggs and the shell porosity. During incubation eggs need to lose a fixed amount of water which corresponds to a loss in weight of around 13-16% depending on species. By weighing eggs periodically during incubation it is possible to monitor and, if necessary, correct humidity levels to achieve the correct weight loss.

Weigh the eggs on the day they are set in the incubator, take the average weight and plot this on a graph (see example below). The ideal weight loss line can be plotted by joining the point representing initial average weight with the ideal hatch weight (13-16% less depending on species) with the x-axis representing the incubation period (in days).

By measuring actual average weights every few days the actual weight loss can be plotted and compared to the ideal weight loss line and corrections can be made. For example if the actual weight loss was greater than ideal (see graph below) then the air has been too dry and humidity levels need to be increased to compensate.

Of the two methods given above the most reliable is egg weight method and is recommended – particularly where poor hatch rates are experienced or if eggs of high value are being incubated.

Alter the setting of the ventilation control (reduce ventilation to increase humidity) and have water in neither, one or both of the water channels to change the humidity level. Humidity levels may be further increased by placing strips of evaporating card or cloth into one or both of the water troughs, or follow the instructions of the incubator that you are using.  Instructions may differ.   

In all cases the humidity for hatching needs to be high to prevent the shell membranes to dry out which makes it very difficult and sometimes impossible for the chick to emerge. When they dry out they become like leather.

Because of the short duration involved water/weight loss will not be significantly affected. High humidity is necessary to prevent membranes drying and hardening before the hatch fully emerges. Humidity will naturally increase as the first eggs begin to hatch and internal membranes begin to dry. This effect is in addition to the increased area of water evaporation from the water channels.

During hatching the high humidity levels will fall dramatically when the lid is opened and will take some time to build up. Resist the temptation to lift the lid frequently – leave for at least 6 hours between inspections.