I have 3 six month old hens (no roosters) and two of them suddenly lost feathers around the vent with some blood present in the bald area, the third hen was perfectly fine. I took them to the vet and had blood, throat, and fecal cultures done and everything was normal, the vet also told me that there were no signs of lice or mites. The vet then started going over their environment and food and the only change made was placing them on a sand run just 6 days prior to this starting??? I've done a lot of searches on this forum and on google and found this bald vent issue mentioned many times but no definite fixes. So as the vet suggested I took them off the sand (just bought 1250 lbs. of sand!!) and placed them on a grass run and now the bald area is much better and is filling in with pins!!! I also found this article on the web stating that sand instead of straw or wood chips increases cannibalism. http://www.plamondon.com/faq_healthcare.html Could the sand really be the cause??? I would be very curious to find out from other people with similar problems with their chickens what kind of run material they're using.