I get an attack of the irritations every time I see advice about the
'need' to rot horse manure..I always wonder about whether the person
giving the advice has ever experiemented or is just parroting book
learning.

It doesn't need rotting at all, ever. It may need some judicious
thought about placement but it can go on some spot or other in the
garden straight from the end of the horse's alimentary canal. I know
because I've used it that fresh and never found any detrimental
effect. It may not look pretty and the well rotted stuff does look
prettier but with mulch on top, who cares or will even notice?

I have a small muck heap near the stables and a big one in the corner of
the paddock but at this time of year when the ground is wet I have
chucked it straight onto the garden or any available bit of ground, it
has never caused any problems I just dont usually admit to doing it :-)
kate