Any experieinces that you may be able to share?
I've been looking online about using horse manure in our multi fuel burner. It seem's it's possible if not a bit of work but seeing as we have limitless supplies, I'm willing to give it a go! 
Ye gods you'll stink the area out for 15 miles down wind if you do burn it... might even get some beared sandal wearer or potential ex townie complaining they can't eat their nut cutlets because of the stink when they press the local council to prosecute you for causing a statutory nuisance .
You have said " Horse manure " ..I take it you mean mixed with urine soaked bedding not just neat lifted off the field in a paddock clear up and well dried .
If it is even slightly damp it stinks of very strong horse sweat and pee , burning it produces enough moisture to activate things .
I've used bone dry cow pat in my smoker for bees when I ran out of my normal fuel ( used to run 50 hives plus 40 neuc boxes ) and even that smoke was still slightly damp , ammoniated / urineated as well as very herbal .
In 1995 I tried to burn a massive heap of rabbit muck and bedding out in the field in stages that was there in place when I moved to my last small holding .. I got a visit from the environmental health because of complaints from several people well over 1 3/4 mile down wind .. I had to put it out there and then or face prosecution as it was on a stop right now nuisance notice . I used my big hot water pressure washer to put it out and boy did it stink until it was cool.