I made a messy concoction of vinagar, garlic, a bounce fabric softner sheet and some leave in human hair conditioner. Put it through a strainer cut it half with water and sprayed it on. It did actually work. It was such a mess making it I decided it was easier to buy Pyranha fly spray. That's the best in my opinion. I read someplace that feeding your horse garlic and adding vinegar to the water helps too, but never tried it.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France