I typically use horse manure in the fall and let it breakdown all winter and spring. There's a horse boarding farm less than a half mile away, and I take 5 gallon buckets there and get it for free. I usually dig from the bottom of the pile too, to get the older stuff. This year a woman I work with gave me 20 gallons of chicken manure that I tossed in there already.
also, I think cow manure isn't that great. Since their stomach breaks it down so much, their manure doesn't have a lot of value to it.