how critical is humidity?


In the Brooder
10 Years
Sep 13, 2009
Bellville TX
i will give a senario,first let me say im no newbie to hatching in an incubator and have great hatches-ok here it is,down in lets say houston tx in the summer you have a broody hen setting in 95 deg weather with a rel humidity of 90% for the whole 21 days why is it with that high of humidity you get excellent hatches,why are we so critical about our numbers inside?does the hens body suck moisture from the eggs?tell me what you all think.
I don't have the answer, but I have been doing the "dry incubation" with my incubators. I am in AL so we have that dripping humidity too. I am having excellent hatches, and I don't have to worry about the humidity until the 18-19th day of incubation.
Maybe the warm feathers of the hen soak up the moisture.
I think its the hen's skin that keeps a constant humidity, and with that said, is a hen really smart enough to stop turning eggs on Day 18? No way those eggs dont get moved around the last few days under her.
So glad you posted this! I set my first incubator last week and was shocked that I had sky-high relative humidity! I am waiting until the last couple of days to bump up the humidity. I have 30-40 percent without any additional water added in the incubator.
I live in the desert in Arizona and the humidity level on a good day would average 14 to 16 percent. So humidity in my bator is a MAJOR factor. I found this out the hard way. I wait until the moment they pip, then I take a sponge and wet it, pop it in the microwave for about 20 seconds. Getting it good and hot, then drop it in the bator. Humidity will instantly climb up to around 85% and the chicks hatch out with ease in no time flat. Without it, the membrane just shrink wraps and kills the chick.
I also do a dry incubation with humidity at 25-35%, bumping it up at 18 days. Have great hatches. My grandmother use to hatch in an metal incubator and all she did was put a cup of water in it. She hatched tons of chicks like this.
I dry hatch and roll them until I see a pip, then I stop rolling add humidity (sponge and cup for mine) and let em work it out.

I know there's a mechanical difference between under a direct heat, moist source - and skin is moist, under a hen and an dry heat source like we use in an incubator that constantly robs moisture from the air.

I don't think hen's stop turning eggs, I've sat in the coop long enough to see a last three days broody retuck and therefore roll eggs and settle again. She didn't get up but she did tuck eggs to better suit herself and I bet a good hen is preventing cool spots/cooler eggs at the perimeter.

Humidity/ventilation is about the individual incubator and the amount of both long term (day 1-18) moisture loss - you need some (12%) but there is a point that becomes more dangerous - over 12% and in some incubators and climates excess loss is too easy.

Some eggs require more care due to moisture loss/heat exposure in shipping.

It's more a matter of learning your set up, observation and reaction than a set number.

My Great Grandmother never hatched a shipped egg in her life, so she never dealt with detached or scattered air cells, rough handling and moisture los/heat exposure in transit.

Hens is one thing.
Artificial Incubation of your own eggs another.
And artificial incubation of shipped eggs a third.

While we shoot for similar values things are always going to be slightly different between them.

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