It's more important to rot down cow and chicken manure, AIUI but I think the
point of leaving horse manure in a heap is to allow weed seeds to be washed
out by the rain or to be taken out by the proud owner of the manure heap. I
think the horse's alimentary canal does a good job of preparing the manure
for use by the gardener.

I am not proud of my muck heap I wish some one would take it away. In
the old days we were allowed to burn them but not any more, pity that,
it smells rather nice :-)

kate