Hello, I have a group of Cayugas that are 5 weeks old. I noticed one duck has progressively lost all the feathers on its back between the wings and on the tips of the wings. It's entire back is bare and has developed some sores. Also, it has extreme trouble walking now. I separated it from the rest of the flock, provide water with antibiotic and sprayed back with blue coat. Does anyone know what is wrong with the duck?