Tiny predatory wasps! No poison, no nasty sticky traps, nothing to put on the animals every day, just let nature do this. I had 8 horses within 100 ft of the house in the middle of Kansas. They were on a 1/2 acre, and belonged to my nephew who never cleaned up the manure (another story). I found a website that sells tiny predatory wasps. Some of the feed lots in Western Kansas use them. They are smaller than a gnat and can't hurt you or the animals. They lay their eggs in fly maggots, which are in the manure, and the wasp larva kills the fly before it hatches. I couldn't believe how fabulously this works!!! It took 2 months before I looked out and the horses weren't even swishing their tails. You need to put them out on manure and repeat it every 3 or 4 months. I don't know if they fly away in between, but I didn't care, it worked so well. Before this, I had flies all over the white siding on the house leaving spots and all over the windows and animals. The chickens and guineas couldn't keep up (BTW throw the fly cocoons out after the birds go to bed or they will eat your wasps). The wasps are so tiny, they are way, way too tiny to hurt you or your animals. About the size of a comma in this post. I guarantee you will use them forever if you try them. Don't use insecticide on the manure at the same time or you will kill the wasps. I got them from Spalding Labs, but they are on Amazon from many vendors. Check the Spalding web site's video. I will never use anything else. They are not free, but they are magic!