## Overview Anhidrosis is the partial or complete inability to sweat in response to increased body temperature or exercise. Because horses dissipate 65 to 70 percent of heat through evaporation of sweat, affected animals are at high risk of hyperthermia, especially in hot, humid climates. The condition is most prevalent in the southeastern United States and Gulf Coast states but can occur elsewhere during heat waves. Onset may be gradual or acute. ## Causes The precise mechanism is incompletely understood. Over-stimulation and subsequent down-regulation of sweat-gland beta-adrenergic receptors is a leading hypothesis. A genetic component is suspected. Temporary anhidrosis can also be induced by macrolide antibiotics. Chronic idiopathic anhidrosis persists across seasons. ## Diagnosis Diagnosis is usually presumptive based on history and clinical signs (elevated respiratory rate, failure to cool after exercise, minimal or absent sweat when other horses are sweating heavily). An intradermal terbutaline or epinephrine sweat test can confirm reduced sweat production. Bloodwork rules out other causes of hyperthermia. ## Treatment The only consistently effective intervention is relocation to a cooler climate, after which many horses resume sweating. Management in hot climates focuses on preventing heat stress: early-morning or late-evening work, fans, misting, and electrolyte supplementation. No pharmacologic or supplement therapy has met evidence-based standards for long-term efficacy. ## Recovery and Prognosis Horses moved to cooler environments often regain the ability to sweat and can return to athletic use. Those that remain in hot, humid climates require lifelong management to avoid dangerous hyperthermia. The condition itself is not fatal if heat stress is prevented. ## Prevention No specific prevention exists. Careful acclimatization and avoidance of peak heat may reduce clinical expression in susceptible horses.
reduced or absent sweating; elevated respiratory rate after exercise; prolonged recovery time; dry, flaky skin in chronic cases; exercise intolerance in heat
## Overview Anhidrosis is the partial or complete inability to sweat in response to increased body temperature or exercise. Because horses dissipate 65 to 70 percent of heat through evaporation of sweat, affected animals are at high risk of hyperthermia, especially in hot, humid climates. The condition is most prevalent in the southeastern United States and Gulf Coast states but can occur elsewhere during heat waves. Onset may be gradual or acute. ## Causes The precise mechanism is incompletely understood. Over-stimulation and subsequent down-regulation of sweat-gland beta-adrenergic receptors is a leading hypothesis. A genetic component is suspected. Temporary anhidrosis can also be induced by macrolide antibiotics. Chronic idiopathic anhidrosis persists across seasons. ## Diagnosis Diagnosis is usually presumptive based on history and clinical signs (elevated respiratory rate, failure to cool after exercise, minimal or absent sweat when other horses are sweating heavily). An intradermal terbutaline or epinephrine sweat test can confirm reduced sweat production. Bloodwork rules out other causes of hyperthermia. ## Treatment The only consistently effective intervention is relocation to a cooler climate, after which many horses resume sweating. Management in hot climates focuses on preventing heat stress: early-morning or late-evening work, fans, misting, and electrolyte supplementation. No pharmacologic or supplement therapy has met evidence-based standards for long-term efficacy. ## Recovery and Prognosis Horses moved to cooler environments often regain the ability to sweat and can return to athletic use. Those that remain in hot, humid climates require lifelong management to avoid dangerous hyperthermia. The condition itself is not fatal if heat stress is prevented. ## Prevention No specific prevention exists. Careful acclimatization and avoidance of peak heat may reduce clinical expression in susceptible horses.
reduced or absent sweating; elevated respiratory rate after exercise; prolonged recovery time; dry, flaky skin in chronic cases; exercise intolerance in heat