I keep a horse on a half acre (it is 1 1/2 acre lot but 1/2 acre is for a large barn, and outdoor storage, a 25 foot stripe is for the goats (3), and 1/2 acre for the horse, the rest is the house, gardens, lawn). Spice gets grazing when the ground isn't a soggy mess, but other wise she has the "dry lot" with her run in, trees, and good footing (sand and small gravel). I pick up manure almost daily, and I "rent" a barn off site to store a years worth of hay, and pick up more and fill my baby barn. I also keep bedding off site, and bring it when I need it. Manure is put in the garden to compost over winter, spread on the pasture, or we have other people come pick it up for free. Flies are bad but nothing we can do because we live next to swamps and they just happen. Fly spray, fly sheets, and traps.
She eats hay daily regardless if she is grazing, just a little less.