I'm new to BYC and not sure if it's effective to join in on an old thread. Is it?
I enjoyed reading this write up on humidity, especially the often debated lockdown methods. I've read so much in the last couple of months as I prepared to incubate my first duck eggs. I've been weighing and canceling and reading, and reading some more. I started at 45% RH, weight loss wasn't enough so lowered to 35. Still not enough by day 18 so lowered to 25. My Hovabator will run at 10% if I add no water. So as day 25 approached, I was just under a weight loss of 13%. Not ideal. So being new to this, I wanted to know why is humidity raised so high 3 days before hatch? I could really use those days to keep it low and reduce moisture. I've kept the temp very consistent so not expecting an early hatch.
I do believe in experience and gut feeling so when I read what experienced, successful hatchers have done, I feel it's valuable information. I also like the scientific method and found great data from various sources that favored a lower humidity to start. And in two highly regarded sources (Storey's Guide and Poultry Keeper) they both say to raise humidity 24-48 hours before the first expected pip "to prevent shell membranes from drying out excessively" and to "help soften the egg shells before piping." I also read that lowering humidity too much at the end causes the weight loss to potentially come from the bird itself like its legs rather than moisture from the inside of the egg. Not sure if this is true.
So my dilemma is, do I continue to keep humidity low to lose those last precise kilograms or do I raise it even though I've only lost 12.5% by day 27 to soften the shell for easier piping?
Sounds like you've done quite a bit of research, so here's my 2 cents worth - they will continue to lose weight, even though you raise humidity. I have found air cell size to be as important (if not more so) than actual weight numbers. Yes, they correlate, but shape of the air cell vs. shape of the egg makes a bit of difference when I make a decision on humidity.
If you feel the need to wait one more day, its not going to hurt. Wait 12 hours, wait 24 hours... There are folks who never raise humidity and have fine hatches. There is unfortunately a lot of trial and error to find what works for you. Local conditions make it impossible for anyone to give you a set number or rule. I could tell my neighbor what would work for her, but I have no idea what would work best for you.
After all that research, you should be able to trust your instinct, and hope for the best!