We have been using Cider Vinegar w/ Mother (sludge on bottom) in it, and the chickens look GREAT! When DW brought it up I thought she was crazy, but I am a convert now - we'd gotten some frizzles/silky's from a local who we bought chicks from and they where looking rough and not in a molting kind of way, so on top of keeping them seperate and treating their issues, we began using the vinegar water and everyone seems to be doing well. Note, Raw Vinegar is supposedly better then the stuff off the shelf in any supermarket, I don't believe that but then again I am using raw vinegar here. Remember vinegar kills germs, here a nice link to pro vinegar side
http://www.aviannetwork.com/articles/acvinthaviary.htm
In the end, I'd say if asked I'd suggest again and again, 100x's again because I can't argue w/ the results I've seen in overall health of my little flock
From
http://msucares.com/poultry/diseases/solutions.html
ASTRINGENT SOLUTION
This solution can be used to treat young birds that show non-typical disease symptoms of poor growth. The solution can also be given to birds suffering from respiratory diseases that produce a large amount of mucus exudate. This solution will help "cut through" the mucus and allow it to be expelled easier.
Two quarts of apple cider vinegar diluted into 100 gallons of water
(4 teaspoons/gallon)
The tannin in the apple cider vinegar aide in removing any mucus or coating from the mouth, throat, or intestinal tract. Nutrients and drugs are more readily absorbed. Offer this solution as the only drinking water source for two to three day intervals.