I have a flock of 19 hens and they all seem skinny. The are healthy, eat well, happy and are in no distress, no mites, lice or worms. What can I do to fatten then up? My DH told me that they just take after their "mom". I am not really worried, but I can always feel the breast bone. Most are 18 months old and have always been thin. Anyone else have the same issue?