03/01/2024
Appropriate Incubation Humidity
I see this subject pop up frequently and the solution to this is a bit complicated. The internet is just riddled with incorrectly given advice and comments. One of the most common methods people mention is “Dry Hatch”, along with others naming specific humidity levels that may work for their environment but do not apply everywhere. In this soap box edition from this overly nerdy chicken rancher, I’ll cover the science behind the effects of humidity levels and how to determine the appropriate humidity levels for your environment.
There’s much science and some math involved in determining the appropriate humidity for a specific environment: Biology, Thermodynamics, Experimentation and Calculation.
Starting with biology we first need to understand the mechanics of the egg and what is happening internally. The shell itself is full of tiny holes and pores, which is where the chick is able to get oxygen through the incubation process. Along with oxygen going into the egg, water v***r escapes the pores as well. As the incubation process progresses, water ev***rates and is replaced by air within the air sack of the egg. It’s important that this air sack grows enough because when it’s time for the chick to hatch it uses the air sack for both a source of air and room to move within the shell. It’s also important that the air sack does not grow too much, as it will dry out the membrane and the chick will become “shrink wrapped” within the shell and not able to hatch. During proper incubation, an egg should lose between 12%-14% (call it 12% for all intents and purposes) of its mass to ev***ration in the 21 day incubation period.
The Thermodynamics application here is the relationship to pressure, humidity, and ev***ration rate. There is an extremely important factor in incubation that is commonly overlooked but has a HUGE impact on the incubation success rate, and that factor is “Elevation”. As the elevation increases from sea level, atmospheric pressure decreases, and as atmospheric pressure decreases, water more readily ev***rates. Because of this relationship, higher elevations will require higher humidity rates in order to keep eggs from drying out too much and losing too much mass.
So how do you determine the appropriate humidity for your elevation and environment? This is where Experimentation and Calculation come into effect. Because of the variability of different environments, the only accurate way of determining the optimal humidity for incubation for your environment is to perform an experiment.
Experiment procedure: Test approximately 10 eggs. It’s important to test several eggs just in case there is an anomaly egg that doesn’t perform properly. The eggs should be as fresh as possible to minimize any weight loss between the time it was laid until the start of the experiment. Weigh the eggs on a tiny scale at the time of start incubation and record those weights in grams. Incubate eggs at a constant temperature of 99.5°F and hold the humidity constant as well. For lower elevations (0’-3,000’) start with a humidity of around 30%-40%, for higher elevations (3,000’+) start with a humidity around 40%-55%. Keeping the temperature and humidity constant is critical. Temperature shouldn’t fluctuate by more than 1°F and humidity shouldn’t fluctuation by more than 3%. IT IS CRITICAL TO KEEP THESE PARAMETERS CONSTANT THROUGH THE INCUBATION PROCESS. If the temperature or humidity fluctuates, so does your results, and your data is no longer good. After exactly 6 days of incubation (to the hour), weigh the eggs again and record their weight. Repeat this on day 12 and on day 18 when they go into lockdown. Based on these weights, you will be able to determine whether the eggs are losing weight too quickly or not enough. This is where the Math comes in.
The Math: An egg should lose about 12% of its mass in the 21 days of incubation. The appropriate weight loss can be easily calculated for the time period that it has been in incubation.
Here’s an example calculation for an egg that has been in the incubator for 6 days. Assume that it weighs 60 grams at the start of incubation.
To determine the optimal total weight loss on day 21 we multiply the starting weight by the percentage it should lose:
60 grams * 0.12 = 7.2 grams
If you divide that over the 21 days you will get the amount of weight per day it should lose, which is the daily loss rate:
7.2 grams / 21 days = 0.34 grams/day
In order to determine the appropriate loss after 6 days we multiply the daily loss rate by the number of days since incubation began:
0.34 grams/day * 6 days = 2.04 grams
And finally, to determine the optimal weight for that day, we subtract the loss from the original weight:
60 grams - 2.04 grams = 57.96 grams
If the actual weight of the egg is greater than 57.96 grams then the egg is not losing enough weight and the humidity needs to be decreased. If the actual weight of the egg is less than 57.96 grams then the egg is losing too much weight and the humidity needs to be increased. This is a trail and error process that may take several incubations in order to resolve the optimal humidity.
After dialing in the appropriate humidity for your environment, you should see a significant improvement in hatch rates.
Happy Hatching!
Colorado based breeder of private line Black Copper Marans. NPIP Certified/Avian Flu Tested.
