What does your vet say about the colt licking the wound? Why not put the colt in a nice dark place during the day and out after dark? Many of the daytime flies aren't out at night. I'd be careful about putting anything on that he will ingest. Perhaps get a real aloe vera plant and squeeze the juice out of it. It helps healing and won't hurt him if he ingests it. It needs to heal from the depths first.