We received our chicks in mid december and began raising them in our house laundry room. My husband built a nice cage and we got an artificial brooder. We have been ffeding them crumbles and all 13 have looked healthy and strong. A couple had some missing feathers but we didn't think anything of it. In the past 3 days we have lost a chick a day. We are down to 10 chicks and not sure what it going on. We cleaned the entire cage and now have them on tetracycline. They all are active and eating and drinking. What is going on? Any ideas?