you will have to use enough to take into account the cattle or it wont help much, I use a multi pronged attack,
I feed textured feed to my horse, and have a doxzen or so free range chickens, the chickens scatter the manure looking for the seeds that pass through, so no manure breeding grounds,
I set out 5-10000 spalding lab fly predators,
I use the proper fly traps, the add water and smelly fly traps don't work. They lure in house and garbage flys but not the flys that bite. You need the biting fly trap traps, look at spalding labs websight on traps they tell you about the different kinds.