The short answer for a Thoroughbred in extreme heat
A Thoroughbred needs exercise cancelled or shifted to first light, unlimited cool water, shade with air moving through it, and several hands-on checks a day, because this breed runs lean, hot, and high-strung and loses condition fast once heat dulls his appetite. A fit Thoroughbred, or one recently out of racing, also generates plenty of internal heat from muscle alone, so he can overheat standing in a humid paddock, not only under saddle. Treat the heatwave as a management problem you schedule around, not a test of how much weather he can tolerate.
Why a Thoroughbred overheats differently
A Thoroughbred's fine coat and thin skin help him shed heat in mild weather, but his metabolism works against him when nights stay hot too. Many Thoroughbreds are excitable in a yard: they fence-walk, weave, call to companions, and burn energy that a quieter cob would save, and every restless circuit of the paddock raises body temperature further. Sweating is his main cooling system, so a Thoroughbred who has gone dry-skinned in hot weather, especially one recently moved from a cooler climate, has lost his chief defence and needs watching far more closely than a horse still lathering normally.
Rebuild the day around the cool hours
Ride or lunge a Thoroughbred before the sun is properly up, and skip work entirely on the worst days rather than shortening a session in midday heat. Turn out overnight if your yard allows it, and bring him into a shaded, ventilated stable or under a fan during the peak hours, because a restless Thoroughbred turned out at noon will often pace instead of standing in the field shelter. Keep two water sources filled and scrubbed, since a fussy drinker may refuse a warm, stale trough, and offer electrolytes in feed or a separate bucket alongside plain water, never instead of it. Split hard feed into smaller meals and consider soaked hay, which gets extra water into a horse whose appetite has shrunk.
Cooling a Thoroughbred who is already too hot
Move an overheated Thoroughbred into shade and hose him continuously with cool water over the neck, chest, and hindquarters, scraping the warmed water off and reapplying so heat keeps leaving the skin. Walk him slowly in a shaded, breezy spot between hosing rounds if he is steady on his feet, and offer small, frequent drinks rather than letting him gulp a full bucket at once. A fan aimed at a wet horse in the stable speeds evaporation noticeably. Stop and reassess if he seems dull, wobbly, or uninterested in water, because those changes mean home cooling is no longer enough on its own.
Heat signs in a Thoroughbred that mean the vet today
Call your vet promptly if a Thoroughbred's breathing stays fast and shallow after half an hour at rest in shade, if his skin stays dry while companions sweat, if his temperature keeps climbing despite repeated hosing, or if he stumbles, stops eating entirely, or produces very little droppings and dark, scant urine. Note the times of each check and what you did, so the vet hears a clear sequence rather than a worried summary. Keeping that running log beside his stable routine is where KinsLe Care Teams earns its place, because whoever is on the yard can see which Thoroughbred checks are done, which are due, and hand the pattern straight to the vet.