Their comb starts getting lighter. Then i noticed they have lost weight although they have been eating. Then they lay on their side and cant get up But can move their legs then die. It takes about a month and is a slow process. There are no breathing problems or outside parisites. Their cages are cleaned several times a week and the feed dished cleaned daily. They all free range for 16 hours a day. They are feed purina chick starter. Used corid as a preventative. No diareha until towards the end. Used wazine to worm them. They are kept very clean and in very clean living quarters. I also rake the free range area every day. Have been loosing a chick a week for several weeks. What could it be?