old chicken coop mulch - gold or better for flowers?

I have an OLD chicken coop on my property that hasn't held chickens for at least fifteen years. It probably has two feet of straw and droppings in the floor. Did I strike gold for my garden (or maybe too old to have value) or is there some reason I shouldn't use it? It's been covered from the rain and is very dry and just smells dusty.

I'd take a wheelbarrow full and get it wet and wait 5 days to see if it heats up.  If so, it's probably too hot to put right on the garden.  

Regardless, I'd spread it around any trees/shrubs you want as a fertilizing mulch.  If it doesn't cook when you get it wet, you could put it in your garden as well.

At least that's my thinking...