The other day, I noticed a small sore on my gelding's cheek. I treated it with Liquid Bandage and put a fly mask on him. The next day, the spot was larger so I cleaned it with water and put more liquid bandage on it. Now it's really big and has little holes. It's gross. There are only 2 horses in this pasture, and cows next door. My other horse has no sores. What is this???