Garden Accesories!!

Hey,
I have a garden in front of my home. I too had a horse and I used to get some manure from the horse. And it was stored in the backyard of my home.
Now, this manure has been too old and can I use these to enrich my soil. I'm having a doubt regarding the quality of the manure as it is old. I shared this with my friend and he was also confused about using the old one. He also suggested me going to this shop offering garden accessories . Does anyone here have any idea regarding this? Please do reply