I do mine the lazy man's way. I just use dry yeast to ferment it. At $4/2lbs, it's worth it, since 1lb will last about 6 months. It cuts the feed bill down by quite a bit actually. I'd say I feed about 75% if I feed fermented and 100% if I feed just wet. For the yeast method, I just put my mash in, sprinkle some yeast on top, mix it a bit, then add warm water and let it sit for a few hours (or feed immediately and use a little more yeast if I've been lazy or busy for that feeding). I like this method better than using ACV and having to strain everything and having buckets sitting around for days. With as much feed as I go through, I'd have to have 15 buckets sitting around every day for the other method.
So it's done to save on feed costs?