Separate the fuel from the animals
Hay, straw and shavings are not just supplies; in fire terms they are the largest store of fuel on most yards, stacked dry and full of air. The strongest protection you can build is distance: keep feed and bedding in a building of their own, set well away from the stables with clear ground between, so a fire starting in the store cannot reach the horses and a stable fire cannot be fed by tons of hay. If one building has to serve both purposes, divide it with a proper fire-resistant wall and a self-closing door, and never store hay in a loft over stabled horses, where heat and smoke rise straight into the space the animals are breathing.
Damp hay is an ignition source of its own
The feed store does not need a spark to catch fire. Hay baled before it has properly dried heats from the inside as moulds and bacteria work in the damp material, and a stack can smoulder deep in its centre before bursting into flame. Only buy and store hay that was baled dry and cured, and be suspicious of bales that feel heavy, smell sweet or musty, or show dust and discolouration when opened. Check working stacks by pushing a hand deep between bales: warmth that does not belong there means the stack comes apart in the open air, away from buildings, before it makes up its own mind. Keep a new crop apart from last year's hay until you are sure it has settled.
Shut out the other ignition sources
Walk the store and remove everything that does not need to be there. Fuel cans, machinery, battery chargers and portable heaters belong in a different building, not beside the bedding. Electrical fittings in dusty agricultural buildings deteriorate, so have them inspected, keep bulbs and cables clear of stored material, and sweep down the cobwebs and settled dust that carry flame across a ceiling faster than the bales below catch. Enforce a genuine no-smoking rule anywhere near the store, and think about lightning protection on an isolated building standing alone in a field.
Layout, access and water
Fireproofing includes what happens after something catches. Fire crews need to reach the building, so keep the access lane and gates clear and know how they open in the dark. Note where your water is: hydrants, tanks, troughs and ponds all belong on the mental map you share with anyone helping. Extinguishers should hang at the exits of both the store and the stable block, of the right type, in date, and reachable without walking past the fire itself. Stack bales so an aisle survives; a store packed wall to wall cannot be fought or emptied.
Make the checks somebody's named job
Most of this fails quietly: the extinguisher check skipped, the new hay stacked unexamined, the heater crept back in. Turn the routine into assigned work by putting the monthly walk-round of the store, the stack temperature check and the extinguisher dates on KinsLe Care Teams, where the duty belongs to a named person and its completion is timestamped, so fire prevention on your yard is a habit with a record and not a good intention.