I put topicals on if cuts are still open... but usually not after they are closed over and dry. If it looked infected I'd upen it up, but it doesn't really. It didn't look fresh, for all I know he may have had this already and it went un-noticed last night when we put them in.
FWIW, We don't have flies any more since the temps started dropping.
Lucky you. I'm spraying once to twice a day. Some of the horses still even wearing fly masks.