Lacto Fermentation is a form of anaerobic fermentation reliant on lactobacillus, the same bacteria responsible for kimchi, yogurt, kefir, sauerkraut, pickles, etc.
For fermented chicken feed, the easiest way to make it is to add feed to a five gallon bucket, 1/3 to 1/2 of the way up. Cover with water. Stir. Add more water. Repeat until the feed is fully submerged (this step is necessary because feeds tend to absorb a LOT of water, crumble most, pellet close, whole grain least). Now add another inch of water. This ensures the process is anaerobic (without oxygen).
Wait.
How long depends on your climate and conditions. A couple days is normal.
I can't describe the smell of a good culture anymore, because I don't have much sense of smell (auto accident - damage extensive), but its pretty distinct, and not really displeasing. At this point, you have a fermented starter, like sourdough.
Scoop out what you want to feed your birds - a strainer helps to keep excess liquid in the bucket where you want it. Replace with an equal quantity of fresh feed. Repeat each day. If the bucket starts to smell bad, something else may be colonizing - start over - but a good ferment ensures so many beneficial bacteria are present that its hard for anything else to move in.
Some people take out "insurance" on their ferment by adding a tub of plain yogurt or a cup of sourdough starter to help innoculate the mix at the start, and most keep a lid, loosely, on their buckets.
Once you've done it a few times, and have a good sense of how much water your feed absorbs at the start, you can mark the inside of your bucket, fill feed to the line, then add water to the higher line, stir and forget.
If you feed as many birds as I do (flock in sig), in a climate like mine, you can line up a couple buckets and get started, one each day. By day three (in the spring, summer, fall) I've got a very good ferment (day two, sometimes) going, and dump the whole bucket to the flock - which I then refill with fresh food and water to start over. The residue on the inside of the bucket helps jumpstart things. SO I can just rotate thru a collection of three or four 5 gallon buckets, not really much more effort than the normal feeding routine.
That said, I do not normally ferment, I usually just offer cold or hot wet oatmeal-like mash. The increased bioavailability of the fermented feed offers a small savings on consumption, but the "looser" consistency compared to my thick oatmeal means I lose more to waste - even serving it in plastic rain gutters - the factors tend to pretty closely balance out for me.
Last notes (speculative, NOT experiential). Fermented feed should *slightly* resist freezing as compared to a wet mash, by a couple degrees. I have hot water near at the edge of my pasture, which is why I do hot/cold water mash depending on season. So that may be a marginal benefit if you are in a borderline region with breif AM and evening temps in the freezing zone. Overnight temps don't matter, since the birds don't generally eat after dark. Second, the colder it is on average, the longer it takes for your ferment to get started on make progress. My temps average around 70 degrees, so a three or four bucket rotation is all I need to feed a flock of 70. If your temps average 50s, you will either need more buckets in rotation, or a longer wait with a much smaller flock.
Hope that helps!
I feed a low/mediocre quality feed, but they free range and get healthy treats. They have been laying more since free ranging. 
