What I started using at the beginning of April is Apple cider vinagre. I give
it in a dosis of 100 cc to all of my horses once a day in their food. Flies
bother them less since then. When they sweat they smell different then
they used to, a bit sour now.
During competition I use 1/3 regular vinagre mixed with 2/3 water in the
bottles of cooling water. This also keeps the (biting) flies away from the
horse.
In the drugstore I bought a citrus-stick against muscitos, normaly for
human use, but it works also well on the horses.
The special fly-liquids for horses overhere are very expensive and
show the same effect as my vinagre and citrus-methods. After a
rainshower effect of both gets less or is even gone, but the food-mixed
vinagre remains effective.
Good luck!
Desiree Hanen - The Netherlands
(Still... it takes Love over Gold & to finish is to win!)