I'm new to cattle but I had such a prob with flys at one time one of my steers has sores on him from the horse flys, I tried a pour on (ivermectin yellow bottle from TSC) but that didn't keep the flys down. I also used (Country Vet CV-80D Flying Insect Aerosol Spray) from TSC, daily or every other day which kept most flys down. Until one day I went old school. I hung a back rub poured a few quarts of used motor oil on it, about a gallon of diesel fuel and half a gallon of insecticide in it. It's been two weeks and at most I see is one fly on them now, where 4-6 giant man eating (lol) horse flys per cow were, now are 0-1 everytime I go out there. I didn't go overboard with liquid in the rub, just enough for a light coating when the cows pass under it. All the sores on the one steer are completely gone, and all 3 of my cows are happy and mostly fly free. I also hung two of those plastic fly trap things, ones disposable and looks like a bell with a cone under it, the other a plastic jar (reusable), them things have caught 2-3 dozen flys each so far ranging from a house fly to a giant man eating horse fly that makes chucky look like a tickle me Elmo. I saw a few warbles in there also, there ok, but the jar one loses water fast, evaporates I'm guessing. So to sum it up, I read back rubs were the way to go with old school guys using motor oil or diesel and my vet said to use insecticide so I said F it I will just used a little of all 3 lmao and I was surprised to find little to no flys on my 3 cows now. Face, legs, back and sides. I'm just glad not to go back there to find a dozen Godzilla sized flys trying to cut steaks out of my cows while 35,000 of there little soldier buddies attacking legs, eyes and for giggles the upper back where the tongue and tail can't reach, (poor cows) I felt really bad for the jersey steer in particular, dude looked like he just watched Hilary become president and was balling his eyes out. (I know politics are touchy here but I couldn't resist lol)