Current weather and delay conditions for (GRU) Sao Paulo-Guarulhos International Airport Conditions
Another option is to mix small amounts of apple cider vinegar with the animal's drinking water; consuming this solution is known to change the blood pH of the horse, thus keeping horseflies away. Cider vinegar, coupled with essential oils, is also used in home sprays as the sharp odor may repeal horseflies.
1 A third design is a flexible curved blade with teeth on one side to use as a shedding blade, and smooth on the other, for use as a sweat scraper.  Fly spray: In the summer, fly spray is often applied to the horse after grooming. Care must be taken to avoid the eyes and mucous membranes.