This hen is about 2 years old and has had this chronic issue. One other hen died and I'm afraid it might have been caused by whatever this is. I only have this fully grown hen, and now have 9 chicks who are 7 weeks old. I don't want to move them in to the coop until this is resolved for fear of passing it on. It doesn't seem to be parasites, and it doesn't look like the pictures of "icky butt" that I saw in the learning center. She is missing feathers and has at times had a very red bottom, in addition to this gunk. She lays nice eggs on a consistent basis, is eating really well, and appears healthy otherwise. I've been putting probiotics in her water, occasionally ACV and giving her plain yogurt. Please advise! PS. I'm a newby to the site!