Anhidrosis — the inability to sweat effectively — is a welfare-significant condition of horses in hot, humid climates that prevents normal thermoregulation and causes heat stress.
Anhidrotic horses experience chronic heat stress in warm, humid weather as they cannot evaporate sweat to regulate body temperature effectively. Elevated core temperature causes physiological distress, reduced appetite, and in severe cases respiratory compromise. The welfare impact is highest in climates where temperatures remain high at night, preventing nocturnal recovery. Management through shade provision, fans, regular hosing, electrolyte supplementation, and reduced exercise during hot periods significantly reduces welfare harm. Severe anhidrosis in a climate where management cannot maintain thermal comfort warrants relocation to a cooler environment.