A Clydesdale's size is the whole heat problem
A Clydesdale overheats because of simple physics: a very large, heavily muscled draft body produces a lot of heat and has relatively less skin surface to lose it through. Add the breed's thick coat and the long feathering around its lower legs, which holds warmth and moisture against the skin, and a Clydesdale in a heatwave is working harder to stay cool than the lighter horses in the next field.
Shade must fit the actual horse. A Clydesdale needs a shelter or tree canopy tall enough to stand under without its back near a hot roof and wide enough to lie down in, and field shelters built for average horses are often too low and too small, so the draft stands outside them in full sun.
Water and sweat: the Clydesdale volumes are not light-horse volumes
Never let a Clydesdale's water run low in a heatwave, because the volumes involved are large in both directions. A big draft drinks far more than a pony or light horse, sweats profusely once hot, and can fall behind on fluids during a single afternoon if a trough is emptied by fieldmates or an automatic filler fails. Check water morning, midday, and evening as a minimum, clean algae from troughs more often in hot weather, and if several horses share a field, make sure the Clydesdale can actually reach the water — a horse standing off because a dominant fieldmate guards the trough dehydrates quietly while the trough itself stays full.
Learn your own horse's normal sweating pattern. A healthy Clydesdale working or standing in heat should sweat across the neck, shoulders, and flanks. A hot horse that has stopped sweating, with dry skin despite a high breathing rate, is showing one of the most important danger signs in equine heat stress, and it changes the situation from routine cooling to an urgent call to your veterinarian.
Work, cooling and the Clydesdale feather in hot weather
Cancel Clydesdale work on the hottest days, full stop. Draft work — pulling, hauling, harrowing — is sustained heavy muscle effort, and the heat it generates inside that massive body keeps rising long after the horse stops. If work is unavoidable, do it at dawn, keep it short, build in standing rest in shade, and finish by walking the horse until its breathing returns to normal before it is turned out or stabled.
Cool a hot Clydesdale with volume and repetition. Apply cool water over the neck, chest, shoulders, and between the hind legs where large blood vessels run close to the surface, scrape the warmed water off, and apply again, continuing until the skin stays cooler to the touch and breathing eases. Pay attention to the feathered legs while you work: that long hair traps heat and hides the skin, so part it, wet the legs thoroughly, and use the chance to check for the cracked, irritated skin that hot, damp feather conceals.
Clydesdale heat signs that need a vet, and a routine that catches them
Treat a Clydesdale that is breathing fast and shallow at rest, stumbling, showing a dull or anxious expression, producing dark or reduced urine, or refusing feed after a hot day as a veterinary call, not a wait-and-see.
A heatwave routine for a horse this size needs more than one pair of hands, and it needs to survive people being away at shows or work. Write the check times, the water routine, and the cooling steps down where everyone helping can see them. In KinsLe's Care Teams, those Clydesdale duties can be assigned per person in KinsLe and marked complete with a timestamp, so the evening helper can see the midday hosing actually happened rather than assuming it did.