Consider it a genetic condition (otherwise why are not all the hatch-lings displaying the same condition if it was an incubation/hatch anomaly as many chose to believe) and cull them from your breeding stock instead of fixing them and letting it hide to breed forward is my sincerest suggestion.. it's not culling for no reason.. it's to me a very good reason, IF I'm the one keeping the breeding stock and hatching more in the future..
Another cause can be riboflavin deficiency.. maybe your breeding stock could use some supplementation.. OR sometimes it's even just an individual that needs a little more help to make eggs viable for hatching even if they have enough nutrients on board for their own health.
Maybe use a smaller based diameter but taller cup??
Sorry I can't be more help.
My comment is my opinion only. Its reflects on my situation and abilities as a chicken lover (we are all chicken lovers here, even with opposite opinions, and thats alright), AND my personal experience this very past weekend.
Im not judging or criticizing anyone or any other opinion. Its just a different thought process than some. It works for me and some other people i personally communicate with daily. It may not work or even fall in line with anyone else thoughts, beliefs or opinions, and thats everyones American right. And I'm all for different thoughts, opinions and communication of such.
I agree half way with EggSighted4Life. Half agreeable with removing them from breeding stock - 100% for sure. Half, not, with culling, if my definition of culling is the same as EggSighted4Life. I may be wrong, but I believe it to be the same across the spectrum of people.
If the chick seems to be otherwise strong (eating, drinking, pooping, sleeping, moving around - even stumbling) and looks to want to be with the other chicks, I say give it a chance to live. It IS a life.
If you have the room, patience and a little dedication, it can have a happy chicken life with other docile, mild tempered chickens. No squabbling or hatching eggs allowed.
I have actually rescued a few splayed chicks and I have had 3 or 4 hatch naturally under hens, over many years of raising poultry. "Under hens" being the focus of that. Some I have successfully helped their mobility, some I could only straighten a little, but it was still better than the start.
None of the double leg splayed chicks have survived. I didn't cull them, I loved them and made sure they weren't suffering. Nature took its course, as it would if I weren't involved.
If you have the room, patience and nerve, they can live and be happy chickens.
I don't breed my chickens, peafowl, ducks etc.. for profit. I will sell some, if someone wants to pay for them, and I have let some hatch, just for certain people who did want to buy some of my chickens offspring. They are an extension of our home and family.
I don't know anything of splaying to be genetic or not.
I'm not here to debate it either, nor will I. I am interested in researching this though. I'm not closed minded.. (calm down grammar police, LoL).
I did, just this weekend, experience a horrible incubation situation where the humidity was very low throughout the whole 21 days, and I had MANY splayed chicks, single leg splay and double splay legs. 3 different breeds. Our poultry, all of them, get supplements and lots of greens, fruits and veggies. Bugs, tadpoles, lizards anything my grandchildren can capture and offer daily.
I don't incubate often, every other year or two. This is the only time I had spraying from the incubator.
Yes, my 2 hygrometers were calibrated prior to putting my eggs inside.. Something was wrong, too late to figure out those details. I tossed the hygrometers and will NEVER incubate ever again. Horrific lesson learned.
I have a separate post called
"Letting off some steam" from a few days back about this whole situation.
My opinion is just that #1, you don't have to cull, nature will intervene. When we aren't involved, nature always does what should be done. 2.) If you intend to breed and sell chicks absolutely keep any and all born defects out of breeding stock, because we don't always know if it's genetic or human error. Don't chance it. Defects from accidents don't count.
Again, these are my opinions and thoughts. It don't line up with everyone's time and abilities.