Opti-Force Fly Spray is a ready-to-use liquid insecticide formulated with cypermethrin for horses and ponies. It is designed to repel and quickly knock down horse flies, house flies, stable flies, face flies, horn flies, deer flies, gnats and mosquitoes, including Culex species that can carry West Nile virus. The formula is built to resist being washed away by sweat or rain, so protection continues between grooming and turnout. It comes in a pump spray bottle and requires no mixing before use, though the bottle should be shaken well each time. For best results the coat should be brushed clean and fully dry before application, and a cloth or sponge should be used to apply the product around the face. Feed and water should be covered during treatment to avoid contamination.