That sucks. Took me several generations before I realized one of my 'imported' males had brought in that splay leg gene. He threw some good scaled chicks too but that was because the mothers were properly scaled. If you've inbred back to the faulty parent/s you'd be much more likely to see this sudden faulty generation crop up. (If this is emerging for the first time, then it will likely be a combination of recessive genes matching up). If you've had spraddled chicks before, suspect the parents even if you thought it was slip-spraddling, not genetic. You'd need to check over your ancestry records to find the hen/s who may have normal legs but might carry the gene. Not all carriers show. But at least one of your chooks, probably the rooster, would show incorrect leg scaling, and likely you've had spraddled chicks from the faulty parent/s before. It's times like these that you realize why you go to such efforts to keep records.

Sadly I think the only way to 'fix' that genetic trait is to cull, but I have a theory that some people with heritage breed chooks have managed to breed this out, or into a different expression. The resulting chooks do not have normal scaling, but it's fragmented so badly their legs are straight, if that makes sense. Right, left, right, left, right, left, when repeated closely enough, equals a straight line. lol. I've not seen this much in Aussie chooks but lots of American ones have it, mostly heritage breeds, hence my theory. Sorry to hear you have this in your flock. I have many beautiful chooks I cannot breed from because of it, and I've culled many more. I'd read SO many ancient and modern books on poultry and never once came across the reason why we are told to 'discard chicks whose leg scales are not straight' --- nor was I ever provided with a sample image of what a straight scaled leg was. All guesswork. Now I can pick up a chick that's wet from the egg and see whether or not I will have to cull. Damage control, now. Shame I didn't know this sooner. I've been trying to find some photos to use as references for others who ask how to check if their breeders have the genes. I've recently found two lots. I hope you don't mind if in future I direct people to this thread as a reference? Or could I cut out the leg part of the image as reference? Feel free to refuse for any reason, it's cool. Best wishes anyway.