Jim
What you describe is not rotted - horse stable manure, it sounds like floor
sweepings out of some dirty stable or barn and I would not touch it, you
could put it in the corner of your garden and it might rot eventually but
not for some time, Where is the straw, horses are not bedded down on hay. If
you do decide to use it ask if the horses are or have been on any medication
or you could be putting all sorts of nasty stuff on your soil.

kate
..

I have just been given a good quantity of horse stable manure. As there is
still a good few weeks before I start planting, will I be OK to dig the
manure into the soil without composting it? It appears to be predominantly
part-digested hay with some urine-soaked hay mixed in. It all appears to be
a good few weeks old. It's not like the well-digested horse droppings that
you tyipcally find on the road where horse-riders have been.

TIA

Jim