I have seen this question several times on this site and others but I am continuing to have a 'vent' problem (loss of feathers and very red bottoms). Just a bit of history: we have 17 chickens, no rooster, clean the pen and boxes every 3 weeks, they have a very large outside running pen and their diet consists of layer feed, a flock block, scratch feed, and all veggie scraps. It started with one and now all of the chickens have the no feather/red bottom issue. We looked for mites at night but cannot see anything, and powdered the pen with anti-mite controll everytime we clean. The flock looks very healthy (minus the bottom issue)and egg production is very good. One keeper suggested a bacteria/yeast imbalance and to use probiotics. Has anyone used this method and did it work? And for those of you who have had this problem, did the vent feathers ever grow back after treatment? thank you.