If you're going to the extra effort and expense to give your flock vinegar, you should get the biggest bang for your buck and the greatest benefits for your birds by purchasing unfiltered apple cider vinegar with the "mother." Bragg's is a common brand, but there are others, and it will say right on the label that it has the mother. For information on the benefits of ACV with mother, Google "apple cider vinegar mother." This type of vinegar is readily available at health food stores and many organic food co-ops. The price is a bit higher, but not crushing. A quart of Braggs runs something in the neighborhood of $3.65 in my area. I use 1 tsp. in a quart of water for the brooder. 2 tbsp. per gallon for the coop/run, so for literally pennies a day, I think it's a great value.