Difference in air sac size for the same hatch

[MidwifeMamaHawk]

Greetings Peeps! (see what I did there?)

I am wondering if some of you may have insight on the air sack size discrepancy between eggs for my current hatch. I am on day 21 of hatching 15 straight run chicken eggs from a friend with a backyard chicken flock.

I am using a Hova -Bator circulated air incubator. I have hand rotated the eggs at least five times a day, but horizontally, not end to end. I accidentally kept rotating them through day 19 but then stopped. I have hatched several sets of eggs in the past, but it has been several years since the last time I did, and since I looked up the proper humidity levels on a chicken feed website, I think my levels were higher than ideal. I kept it at 50%-60%. But it got opened 5-8 times/day so I hope that would reduce some impact of the high humidity levels. I also had all 3 ventilation holes open the entire time.

But the interesting thing here is that one of the eggs, a brown egg, has an air sac size that is absolutely PERFECT! I candled it last night, and I saw the chick trying to pip through the internal membrane. Two small brown eggs have no discernible air sac, and the remaining white eggs all have a very small air sacks. If I ran it at too high of humidity for the eggs, how could I get one egg where the air sac is perfect?

(I am going to post this now, and then will reply to myself with the pictures since I am having trouble posting pictures with this and I don’t want to have to retype it all for the third time!)

Thank you!

 

[MidwifeMamaHawk]

Also, if only 1 hatches, will it be ok to be in brooder alone?

 

[Ridgerunner]

What determines the size of the air sac is how much moisture the egg has lost. That does not mean from the time it went in the incubator, that means from the time it was initially laid. Different things can affect how much moisture an egg loses. It's porosity and the thickness of the shell, how and how long it was stored before incubation began, the viscosity of the egg white inside the egg, and just differences in the eggs. Some of these things will also cause a difference in how fast an egg loses moisture once incubation starts. Also, the temperature and humidity of the air that enters the incubator during incubation has an effect, the humidity inside the incubator, whether it is a forced air or still air incubator, just different things. All this is why different humidities work better for different ones of us.

You are not looking for the best humidity for one egg, you are looking for the best humidity for most of your eggs. Nature was pretty nice to us. She gave us a fairly wide range of humidities that will work for most eggs. But there are still limits. If you are too far out you don't get good hatches.

What I suggest is to try to keep humidity constant when you incubate and keep good records. Assess your results after the hatch and tweak the humidities for your next try based on what you see. It is trial and error but is the same process the commercial operators use. For some of us a 30% humidity works great, for some 55% may be best. I determined my best was around 40% average humidity.

 

[MidwifeMamaHawk]

Baby chick #1 out! Not even externally pipped at 5:30am but was fully out by 7:50am! This is the one that had the normal air sac. Last night I candled the others (which have the small air sacs) and there were signs of life so I made rescue holes and put them back in the incubator so we will see what happens!