I'm really not a huge believer in starting antibiotics unless you have a definitive diagnosis; however, in this case, it might be a good idea. When you say the vent is bulging - are you seeing a prolapse? Are you sure that's what it is? If so, you need to get it back in, asap. The faster, the better. Put some hemerrhoid ointment on it and GENTLY push back in. Then, sort of hold it there for a few minutes; if you've caught it early enough, often times, the hen's musculature in the vent area will hold it in place. It probably will not STAY in place, though, and that's where you come in - you need to check on her often - I would check every 15 minutes - and when she prolapses again, gently press it back into place, holding there for 30 seconds to a minute or longer until she can hold it in herself. You'll see her "twitching" back there and you can sort of feel the muscles trying to hold it in. But, I think it feels to them like a big poo or something and unfortunately they try to push it back out. I had a girl that had a minor prolapse - I caught it in time, left her in a dog crate for several days and kept on putting the prolapse back in. I noticed that more and more time would pass between having to put it back in, and then, after a full day of having it in, I put her back with her flock. I never hd any further issues with her, but I think my success was due to catching it & addressing it quickly. BEST of luck on this!!!
