We have a small flock of 5 and we have two bedding piles - one's a year old and the other is from this year. I take an old pillowcase and fill half of it with the year-old stuff, tie it off, and drop it in a 5 gallon
bucket. I fill the bucket with
water and leave the whole thing - uncovered - in a sunny place for a couple weeks. Makes a sort of fertilizer tea that I then dilute with water in a 1 to 4 ratio (usually 1 gallon tea to 4 gallons of water), then I spray that on my garden periodically throughout the growing season.
So far it's worked great - no burning. I'd imagine if you dug down to the bottom of the pile you'd find some older, more decomposed bedding and manure that might work for this purpose. Although I'm not sure how you'd avoid mixing the newer stuff in. I wonder, though, if a small amount of newer compost might be okay given how diluted this fertilizer tea is.