The best way to control flies is to prevent them as much as possible. Feed-through options are a convenient way to do this. By disrupting the life cycle of the fly they provide effective control. For best results, you’ll want to start feeding them about 30 days before fly season and continue until 30 days after the first frost in the fall. The active ingredient in ClariFly Larvicide passes through the digestive system of the animal and goes to work in the manure. The active ingredient prevents house flies, stable flies, face flies, and horn flies from developing into adults. There are several options available for both horses and cattle that include Clarifly Larvicide.