I have to admit,
I'm not fully intragraded in the hot part
of the composting process..
I know mine gets killer HOT,
but I don't add any
weeds, or
seeds, or roots
to the piles...
Soooooooooooo, I can't say?? For sure...
But, my one base liner around here is
"Experiment"...
Try one pile with it, one pile without it
and see how it works..
Now, you said you also had chicken manure...
That might be your key....
That stuff is hot, and you should only use aged and/or old chicken manure on your
flowers/
plants/garden....
so, if you use it fresh in your compost pile with the horse manure....
That may be your ticket to killing the
weed seeds.
Keep me posted, I'd be truely interested in your
outcome...
You won't see any
seeds, the test will be
the following year in using the compost...