Hi, Mike!! Long time, no see!/w3tcompact/icons/grin.gif
Yep, that's horse manure.
The straw mixed into it is the remains of bedding. I use straw for bedding in my horse stalls.
I spread manure in each hay field as soon as possible after I cut and bale the hay. The manure in that pile ranged from one year old to two months old, but it was pretty well composted throughout. You can especially tell it's well composted, because there was very little straw visible, as most of it had decomposed. Every morning I clean the stalls and remove the manure and soiled straw. You'd be surprised how much of the straw is soaked with urine, and I remove that along with the manure. The pee soaked straw decomposes very fast. I move each manure pile around with my loader periodically to mix it, so it decomposes faster. Besides spreading it in the hayfields, we use it in our gardens, and I even fill the occaisional pot hole in my dirt driveway with it. Our raised bed gardens are filled with 100% horse manure.
It's great stuff to have, and has so many uses! I don't know what people without horses do without it!!!/w3tcompact/icons/laugh.gif