Too fresh I wouldn't be concerned about, just don't apply too heavily or directly. I like to add my horse manure to my compost, it works wonders for the heap, and to my worm bin - they love it! If I use it directly it would be after a crop has come out and while adding mulch to the bed.
My only real concern around horse poo is I like to know when the horses were last "drenched" for worms, because if it is recent I could be carrying worm killing chemicals to my soil, compost and worm bin - not a good mix.
I have bought a large rubbish bin from Bunnings ($15.00) and put the poo in there and filled with water. Leave for a fortnight to kill the seeds. Use the water - about 2 inches in the bottom of the watering can and water on.
Actuall I got an interesting bug in there which I found was a rat-tailed maggot which turns into a hover fly that eats aphids. A bonus!