Sour oats are sometimes called soaked oats, though technically the two terms shouldn't be interchanged. The term "soaked" comes from a way of preparing oats by first soaking the grain prior to cooking or eating raw. The soaking breaks down some natural compounds called phytic acids, which can block mineral absorption. Folk who like to follow a raw food diet often soak their oats in order to avoid this possible problem. If you soak for a long while, a bit of fermentation begins, leading the oats to turn "sour." At this point, the proteins in the oats are more digestible, and the starches too are converted into a more digestible form. I imagine that sour oats would be a great way to bulk up chicken and to provide them with a nutrient-rich source of whole grain.
I've personally never soaked oats, but when I've seen it done it is with whole oats. I suppose that steel-cut oats (sometimes called Irish oats in my part of the country) would work for soaking. The rolled oats are likely to get really mushy.
Use oats like in form of intact seed. You also have activation of some B vitamins making them more available. As I understand it, use of soaked oats was used a lot prior to developement of complete diets.
Try not to have at more than 25% of total diet despite birds being inclined to consume more if given chance.