Have a hen that is severely congested. Separated as soon as we noticed- no others seem to be showing any signs. Hen has a cough, gargly sound. Kind of a bad smell, too. Mucous coming out of beak. Gave Tylan 50 for 5 days. Stopped after 5 took couple days then have started again three days ago. She is drinking water. Eating a little. She is still pretty bad off. Thought she was a goner a week ago, but she is a fighter! Any ideas on what it could be?