I used just plain garlic for awhile. It was an actual horse supplement, I forget the name, but I can check for you. But I'm not sure I noticed much of a difference, except my horse's breath really smelled
I've also tried the Equi Spot stuff, its like flea and tick medication for dog and cats. Its a liquid that comes in a little applicator and you put some a the poll, along the topline, and down each leg. I did notice a difference there, I still applied fly spray, but I think it was nice as just a little extra protection.