If it is that old you can use it as is. ;)

Dave

Use face mask when loading and unloading. Horse manure is fine but some of the other things in old barns can give you a bad chest infection, histoplasmosis for one.

My inclination is to always compost any animal manure before spreading it on the garden, no matter how old that manure is supposed to be. I would just rather not potentially expose my family to disease pathogens if I can prevent that.