While it has probably lost almost all of its nitrogen, it is still organic matter.
Something in your soil will want to eat it, and it will help your soil to hold water.
It should also be totally safe to use as mulch on young seedlings.
I agree with John Polk.
I've used several year old horse manure without a problem.
While loss of N and leaching of nutrients is likely to have occurred, the material would still contain a good deal of hummus. It should make an excellent soil conditioner.
Seed the Mind, Harvest Ideas.
http://farmwhisperer.com