Horse flys in sheath... Help?

his sheath may need to be cleaned(once its healed) if they are attracted to it that much. Obviously it is dirty if they are attracted to it that much. I use endure and it is the BEST fly spray I have ever used. It has a silicone base so it stays on even when they are sweating(again, don't spray fly spray on his sheath until it has healed). Good luck!