When incubating eggs there are quite a few variables to control for a successful hatch, but there are 4 primary factors that any successful incubation must consider: temperature, ventilation, turning and lastly humidity.
Humidity is by far the most difficult to get right and is commonly misunderstood.
The Importance of Humidity
An egg shell might look solid but it is actually very porous. Directly under the shell are two membranes. Between the membranes is a small air cell, also called an air sac, filled with oxygen. As the animal develops it uses the oxygen, which must be replenished, and it also has to release carbon dioxide. In a sense humidity controls the "breathing" or respiration of an egg and the size of the air sac during incubation. While eggs incubate they will naturally lose weight. Humidity controls the rate of weight loss via the size of the air sack so the ideal humidity level must be identified and maintained throughout the entire incubation period.
Probably the most common mistake made is having too much humidity in the incubator. This creates an air sac that is too large inside the egg meaning less space for the chick to grow. The chick will be small and weak and will either no be able to break out of the shell and die or die shortly after hatching. Humidity that is too low makes a small air sac allowing for a larger chick but creates other health problems due to inadequate exchange of oxygen and carbon dioxide during development.
Adding to the complexity of the humidity conundrum is that the ideal humidity differs somewhat between the breed of bird. For example:
Chicken: 40%-50% for first 18 days, 65%-75% for last 3 days
Duck: 55% - 65% on average for 28 days
Goose: 50-55% for the first 27 days, then an increase to 75% for the remaining days.
Turkey: 55% for the first 28 days, then an increase to 75% for the remaining days.
As you can see that while similar the are small but important differences in optimal humidity % depending on the breed of the bird.
The best and easiest way to ensure correct humidity no matter the breed or ambient conditions is an incubator with humidity control. By far the best egg incubator humidity control system on the market today is the Nebula seen below. This ultrasonic humidity generator with microprocessor control is extremely accurate and quickly adjusts in real time humidity % up or down to maintain the desired set point.
The Nebula is a very welcomed addition to any incubator being used in very dry climates such as Colorado or Arizona where it can be almost impossible to achieve the higher humidity levels
The Nebula is designed to work with our EggTech incubator from River Systems (Italy) but can also be used successfully with just about any brand of egg incubator
EggTech Automatic Incubator: