I started using ACV to see if it would resolve the watery poop of one of my six chicks. I knew it wouldn't harm them. It seemed to work (until I put them on the grass one day in a cage; I don't do that anymore as they are too young). I'm switching over to Chick Boost Probiotic as I read it was better than ACV.from my research there is no evidence that ACV is beneficial for chickens and the only proof there exists is that it was considered beneficial for human health but again there is too little evidence to back up this claim either so ACV is just a chicken myth that has cropped up over time. There is no downside to using ACV and it has got trace amounts of vitamins and it can lower the ph of the water slightly and possibly prevent bacteria growing as much but honestly there is no proof it is beneficial in the small quantities used. I just don't really bother with ACV as many others. If there were a real benefit then I would