Thanks fancy, do you wipe their butts every day even if their vent part is clear but its still hard all around it? If thats the case it would be like this everytime they pooped lol. Can they spread it around to the chicks who dont have it? So adding apple cider vinegar to very young chicks is perfectly safe? I think their waterer is a quart. Its just the small basic red chick feeders you get anywhere. Would I just put a half teaspoon in there? And whats the benefit of doing this, how does it help? And what causes pastey butt to even happen? Is it a bacteria?
You will need to wipe them until it has gone. Acv lowers the PH levels and bacteria in the gut. Smear some Vaseline around the vent to prevent poop from sticking to the fluff.