I saw mention of traps, just an FYI, those bait traps dont work, well you will see them fill up with flies, but they arnt the type of flies that bite. They are the typical flies that hang around garbage, the lures do a good job of luring flies in that wouldnt be their to begin with if not for the scented lures.
You want to look for the biting fly traps, these are usually reflective, with black on them to heat up a bit higher than ambiant and have a sticky surface. They are put up low to the ground, like horse ankle high.
But yep they are bad this year. I never had large horse flies this early. FLie management is a multipronged approach.
Step 1 Manure management. You cant have breeding grounds left lieing all over the ground or in a pile. I feed textured feed and the chickens scatter the manure everywhere as soon as it hits the ground. But one way or another you gotta get it spread out and dried weekly.
Step 2 larvae management. Pass through controls, fly predators, (which may be mutually exclusive)
Step 3 adult management. Proper fly traps that target the types of flies you want to get rid of. Area pesticides. (again maybe not good to combine with chickens or predators)
Step 4 Horse protection, Indoor dark ventilated shelters, fly spray, fly sheets, leg wraps. bout it that I can come up with.