We have ten hens, 4 are Silver cochins and 6 are Partridge cochins, and all are almost a year old. For a few months now, we have noticed that all of the partridge cochins look like they're in pretty bad shape, with feathers askew and bald spots mainly on the back of the neck and their backs (2 in particular have very bad bald spots). They have not made much progress growing back within months, one is starting to recover but the other one looks just the same, no feather regrowth at all. the grey cochins look beautiful and their feathers are perfect. We have never witnessed any aggressive mounting behavior from the other hens, nor have we found clumps of feathers in the coop or the yard (they are free range on weekends). They are fed Dumor Pultry Layer Crumble for Egg Laying Hens, and are free to eat what they find in the yard, and we often feed them fruits and (vegetable) kitchen scraps. Also worth mentioning is their egg shells, we usually get between 7-9 eggs per day, but there is always one or two in the batch with incredibly weak or already broken shells. These weak eggs are often coated in a gross yellow liquid as well. Any help would be greatly appreciated, thanks!