My friend's chicken has a Prolapse vent. I helped her clean t it up and put it back into place (though she's still not 100%). Mom said that what we did could count as school if I did research and wrote a report on it and what to do...so here I go.
A Prolapsed vent is where the oviduct (where the eggs are made) comes out of the vent. This prevents the chicken from pooping and laying eggs. There is often chicken poop oozing out and all over the feathers around it. There may also be blood present. The hen will most likely be calm.
The area around the vent needs to be cleaned with warm water and the tissue coming out has to be disinfected. (We used Dial disinfectant soap)
Next you can put something on it to help with pain and swelling. I have read many different suggestions for this, we used antibiotic cream and Vaseline because that's what was available. You can also use Preparation H cream or honey.
Then (the fun part) You need to use your finger to push the oviduct tissue back into the bird. Gloves come in handy here! Once it's in you might want to hold in there for a minute until she stops trying to push it back out (you can tell by feeling it against your finger), Put more cream on the outside once its in.
If it wont stay in place (we had this problem) you can diaper her over night. and that should cure it; although is is common for the issue to arise again later so keep an eye out for it.
Only bandage/diaper the bird over night! if it's on during the day she wont be able to lay her eggs making the problem worse. Here's a link on how to bandage the prolapse: http://www.littlehenrescue.co.uk/Pages/Medicaladvice.aspx
A Prolapsed vent may be caused by a number of different things; it could be because the hen started laying when she was too young, or maybe the chicken laid an egg to big, soft or weird in shape, if the chicken is old and over weight it can also cause it. Or there might be an egg stuck. If you think the last is the case you can gently massage around her tail and vent to see if you can feel and egg.
Another possibility is the chicken is deficient in calcium.
After the treatment add vitamins, electrolytes and/or liquid calcium to her food or water; and keep her away from the flock until the issue has cleared up completely.
If the other chickens are able to pick at her vent they could make it worse infecting it and possibly causing her death.
Your chicken may also need antibiotics if it's really bad.