Update: the original hen from this post is getting better...but now I have another one...so apparently I have a hen that is doing this to them...what would cause this behavior? The hen I found today isn't as swollen as the first one was, but her feathers have been pecked off and she is bleeding.... she is getting the same Epsom salt bath and antibiotic ointment treatment as suggested.
Chickens will peck at anything they see that is strange on another chicken— that’s pretty normal behavior. It can become an obsession with a bird sometimes, so you
always want to discourage it.
I think you need to give the girls with the red butts some extra calcium. You can use human calcium pills— Caltrate (calcium
citrate) with vitamin D3 is the easiest for them to absorb... but you can use Tums (calcium
carbonate) instead (yes, the antacid tablets... bonus, no hens with heartburn.

)
- Caltrate = 1 tablet given whole or split/crushed/dissolved
(For soft eggs, or egg-binding—1/2 tab should be given daily for minimum of 3 days, or until a normal egg is laid + 3 days)
- Tums = 2 tablets given whole/split/crushed/etc.
(as above —> follow with 1 tab daily (for same times as above)
So the reason I believe they need calcium is that I think they are having slight prolapse after laying an egg. Calcium isn’t just for making hard shells... it‘s also crucial for helping the muscles throughout the oviduct & vent work properly. A prolapse means the hen is needing to strain when laying. A dose (or a few doses) of calcium won’t hurt them, but it could help their muscles work efficiently again.
For the current protrusions, Preparation H hemorrhoid ointment generously applied to all the puffy, red vent area will take away the swelling & inflammation, and it’ll go back inside.
If you have blue-kote you can spray their bottoms when you put them back outside, so that whoever your bully is won’t be attracted to the redness.
If any other hen-pecked girls show up, you may need to crush a few calcium tabs and mix it into their food. Or you can dissolve a few tabs in a little water and then use that to wet a small amount of their feed. Divide it into a few dishes so that they all get some.
So long as your bully hasn’t become obsessed, you should be able to get it under control with what I suggested above.
Good luck, & keep us posted.
