There are a few methods in using ACV, it depends on why you are giving it to your birds, if you're using it as a repellant for worms, you must feed it every day, it acts on the fact it changes the gut Ph to acidic, where worms don't like to be, and if it's not given in a maintainance dose, it simply won't work.
I have been using acv for many years with no ill effects, but it has to be said it is an astringent, although a natural product you can overdose with it causing liver problems, so it must be measured carefully. Using neat in feed i haven't tried, but as long as it's mixed thouroughly it shouldn't cause a problem when measured correctly.
The dose is as follows:-
To worm, for 7 days one week a month, = 25mls per litre of fresh water (large fowl) and 20mls per litre for bantams.
Maintainance dose for 3 weeks,= 15mls per litre of fresh water (large fowl) and 10mls for bantams.
To aid with coxy= 30mls per litre of fresh water for all birds, until a coxy medication such as coxoid or baycox can be administered.
Given everyday it is only like us taking a multi-vitamin, if you don't take it everyday, you won't have the benefit of it working properly. But as with most things, be careful to give the right dose.
As mentioned above, waste is down to the keeper, if you find that you are tipping alot of water and ACV down the drain each time, then use smaller drinkers. I have 12 paddocks, and various different bantam pens, and a 5litre tub of ACV lasts me a few months. I use it all the time. If your drinkers get slimey and green, move them to a shaded spot if possible to prevent this. And change the water daily. I change my water every two days, using fresh tap water, and mine don't get slimey!
I do welfare talks for Pets at Home and various other places, i have an ACV information leaflet, if anyopne would like one, please PM me your details, and i will post them a copy, or email them it. It contains all info on using ACV, and the dose instructions.
JubesXX