Hi, I am new member to backyard chickens. I have 9 chickens for past 4 years. They have been healthy until last 6 months noticed one chicken losing bottom feathers and has discharge stuck to vent. She is eating and drinking and free ranging fine. Seemed to come and go, but now it is worse and her other feathers around neck are not as full. Now noticing some of other chickens have some mild discharge around vent but nothing dramatic. Just want to prevent further disease. Not sure what it is. Chickens otherwise doing well. Thank you for any help/recs you all can give!