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Hot and humid conditions present a unique challenge for horses because humidity dramatically reduces the effectiveness of evaporative cooling from sweat, leaving horses in the southeastern United States at high risk for heat stress due to the combined effects of metabolic heat production and impaired heat dissipation. During intense exercise, up to 80% of metabolic energy is converted to heat, causing rapid increases in core body temperature that must be dissipated to avoid hyperthermia and heat-related illness. In humid environments, traditional thermoregulatory mechanisms — particularly evaporative cooling — are significantly compromised, requiring targeted, evidence-based cooling strategies.
During exercise, only about 20%-25% of the energy generated by muscle contraction is converted into movement, while the remaining energy is released as heat, creating a substantial thermal load that must be dissipated. Horses rely primarily on evaporative cooling through sweating to remove this heat. In humid environments, where the air is already saturated with moisture, evaporation is markedly reduced and sweat may drip from the body rather than effectively carrying heat away, resulting in inefficient cooling despite heavy sweat production. Consequently, core body temperatures can rise rapidly during intense exercise, often exceeding 105.8 F-107.6 F. Without prompt and effective cooling, these elevations can impair cardiovascular performance, disrupt gastrointestinal integrity, compromise neurologic function and delay recovery, potentially progressing to exertional heat illness or heat stroke. Early recognition of heat stress is critical, as horses may deteriorate rapidly once thermoregulatory mechanisms are overwhelmed. Common clinical signs include:
In hot and humid environments, effective cooling strategies must account for the reduced efficiency of evaporative heat loss, which shifts reliance toward active cooling methods such as conduction and convection. Research consistently demonstrates that immediate, continuous application of large volumes of cool or cold water is the most effective strategy for rapidly reducing core body temperature following exercise, outperforming intermittent misting, walking or airflow alone. Water should be applied directly to areas with large muscle mass and major blood vessels, including the neck, chest, shoulders and hindquarters, to maximize conductive heat transfer, as heat moves from the horse’s body into the cooler water. Contrary to traditional recommendations, concerns about cold-water-induced muscle cramping are not supported by research, and aggressive cooling is both safe and necessary. While airflow from fans or natural breezes enhances convective and evaporative heat loss, it is insufficient alone and should be used in combination with water application for optimal results. The longstanding “spray and scrape” method has also been reevaluated. Evidence indicates that continuous water application without scraping is equally or more effective in humid conditions, as maintaining water contact improves conductive cooling. If continuous water flow is not available, repeated dousing with cold water at short intervals remains beneficial, if reapplication is frequent and focuses on high-blood-flow regions.
In humid environments, the horse’s primary cooling mechanism of evaporative sweating is compromised, requiring active, aggressive cooling strategies. Research supports continuous application of water as the most effective method for reducing core body temperature following exercise. Auxiliary methods such as increased airflow may enhance outcomes but should not replace direct water cooling. Utilizing proper cool down methods post exercise is a vital component to maintaining your horse’s overall health and career longevity.
Foreman, J.H. (1996). Thermoregulation in the horse exercising under hot and humid conditions. Pferdeheilkunde, 12(4), 405–408.
Kang, H., Zsoldos, R.R., Sole-Guitart, A., et al. (2023). Heat stress in horses: a literature review. International Journal of Biometeorology, 67, 957–973.
McConaghy, F.F., Hales, J.R.S., Rose, R.J., and Hodgson, D.R. (1995). Selective brain cooling in the horse during exercise and environmental heat stress. Journal of Applied Physiology, 79(6), 1849–1854.
Takahashi, Y., Ohmura, H., Mukai, K., et al. (2020). A comparison of five cooling methods in hot and humid environments in Thoroughbred horses. Journal of Equine Veterinary Science, 91, 103130.
While horses rely primarily on evaporative cooling through sweating to remove heat after exercise, humid environments can make this more difficult. Photo by Joseph Bergeron
P4081
9/25/26
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