More details about prolapsed vent causes, prevention and treatment can be found on my blog here.
1 Damerow, Gail (1994). The Chicken Health Handbook. page 53: Storey Publishing.
2 Anatomical illustrations and photo reproduced for educational purposes, courtesy of Jacquie Jacob, Tony Pescatore and Austin Cantor, University of Kentucky College of Agriculture. Copyright 2011. Educational programs of Kentucky Cooperative Extension serve all people regardless of race, color, age, sex, religion, disability, or national origin. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, M. Scott Smith, Director, Land Grant Programs, University of Kentucky College of Agriculture, Lexington,and Kentucky State University, Frankfort. Copyright 2011 for materials developed by University of Kentucky Cooperative Extension. This publication may be reproduced in portions or its entirety for educational and nonprofit purposes only. Permitted users shall give credit to the author(s) and include this copyright notice. Publications are also available on the World Wide Web at www.ca.uky.edu. Issued 02-2011