In the last month I've had four hens get sick and two died before I started bringing them inside. They start out lethargic, then stop eating and their eyes start matting shut and swelling. Two died before I noticed the problem, I brought the next four In the house, fed and watered them with with a syringe and tubing. I dosed them with pennicillin twice a day and two have recovered and are back in the pen. All the sick hens are/were about 2 years old, are cooped in a semi climate controlled coop and have free access the outside. The flock is about 40 birds. Anyone know what this could be?