I've used horse poop around all my plantings... I haven't seen any problems.
On the other hand... I've seen people kill stuff with those chemical fertilizers...
And, the poultry manure from the commercial broiler houses can be deadly when used as a soil conditioner... but used extremely lightly? No probs...
Horse poop is ideal as a soil conditioner... there just isn't enough nitrogen in the stable scrapings around here to bother anything...
Although... using stuff that has too much wood shavings in it... is a whole nother art form...
It isn't that it has nitrogen in it... the potential problem is that those wood shavings pull nitrogen away from the plants!
So... I use that as mulch... in a couple years or whatever, it can be tilled in if desired.