Schering - (Organophosphate) Super Kleen releasing agent, Dominator releases insecticide throughout its affective life span. Which means that Dominator ear tags deliver superior horn fly control for up to five months. How to fight resistance: Because Dominator ear tags contain a unique organophosphate, pyrethroid-resistant horn flies have no special defense against it. As long as you rotate yearly between Dominator and pyrethroid, like Saber Extra insecticide ear tags, the chances for future resistance may be reduced. Two tags per head is also necessary to insure that an effective amount of insecticide is being released to control horn flies. Packaged 20 tags per bag.