Safe, effective, feed-through fly control for horn, face, stable and house flies. Can be used with all classes of cattle and horses. Fortified with NRC recommended levels of minerals and vitamins. Convenient, 33.3-lb blocks can be easily placed where needed. Does not affect existing adult flies. Start use in early spring before fly appearance and continue feeding until cold weather restricts fly activity. | Rancher's Choice Clarifly Fly Control Pressed Block | Size 33.3 lbs