A wise old horse friend once told me that a horse can get hurt in a padded stall
But seriously, our mares get little scrapes and cuts all the time, especially in the summer when they are sweaty and the bugs are out from rubbing, branches, their hooves chasing flys, fence posts, ....anything (1000 lbs rubbing on the corner of a piece of wood will make a scratch). If it's not bleeding, just leave it, or a little betadine and neosprorin.
Our mare, Lady, got a 30 stitch cut on her flank a few years ago in a paddock. My wife, the vet, and I checked every inch of that fence and never found anything sharp and not even any hair or blood.
It's one of the mysteries of owning horses.