so i could keep hens and make sure new cockeral is top notch? do you think its caused by in-breeding? never had problem before and kept about 10 breeds before this.
If you mate a normal/rapid (k+) cock to the hens, and if they are Kn (extremely slow), Ks (slow), or K (late), only the resulting cocks will have it.
Are the wing feathers normal? If not, then the hens could be ts or t, these are autosomal genes recessive to normal T, and can only be expressed in the presence of k+. If they do have it, then all resulting young will be carriers for it.
Test mating would be the only way to know for certain.
It may well have absolutely nothing to do with this and be something totally different. Have you ruled out the feathers being abraded by anything?