SimpliFly Feed-Thru Fly Control prevents development of house flies and stable flies in the manure of treated horses. This product is palatable, just add to feed - and contains no organophosphates. It breaks the fly life cycle by preventing the formation of fly larvae exoskeletons when they molt (resulting in their death). This is the ONLY feed-thru fly control for horses granted reduced-risk status by the EPA. | Farnam SimpliFly Feed-Thru Fly Control for Horses | Size 10 lb