During hot weather, heat dissipation is primarily dependent on evaporation of sweat on the skin surface. Horses are capable of producing large quantities of sweat—sweating rates of 10-15 liters/hour¹ have been reported during exercise in hot conditions. Sweat evaporates efficiently in hot, dry conditions, but not in hot, humid climates that are likely to impose a particularly large heat load because heat dissipation is compromised, and the horse retains heat. In addition, horses have a large muscle mass and a comparatively small body surface area. This configuration results in a limited surface area for evaporative heat loss.

Clinical Signs of Overheating

Lethargy, unwillingness to perform as expected, a persistently high rectal temperature, and moderate to severe dehydration might be observed in overheated horses. They are usually disinterested in the environment, and they might not voluntarily eat or drink. More severe heat stress is associated with exhaustion, increasing body temperature, decreasing blood pressure, and collapse. Heat stress has deleterious effects on many organs and can be life-threatening.

Helping Your Horse Cope with the Heat

  1. Consider clipping horses with robust body condition, a heavy hair coat, and few visible veins on the skin before hard exercise.
  2. Condition your horse for the intended exercise. Physical fitness is essential for coping with heat during exercise.
  3. Allow your horse to acclimate to hot weather for 10 days to two weeks before riding long distances or training hard.
  4. Be sure your horse stays well-hydrated. Provide two water buckets and 24-hour access to as much water as he wants.
  5. Give a salt supplement if you are working your horse regularly during hot weather. Avoid supplements that have sugar (dextrose) as the first entry on the ingredient list.
  6. If possible, allow your horse to drink during lul