What should be considered a sign that a horse is overheating?

Excessive sweating is indeed a clear indicator that a horse may be overheating. When a horse is physically exerted or exposed to high temperatures, its body temperature rises, and sweating is the primary mechanism through which it tries to cool itself down. If a horse is sweating more than normal, especially when not performing strenuous work or in cool conditions, this can signal that its body temperature is rising to unsafe levels. Observing excessive sweating, especially in combination with other symptoms such as rapid breathing or lethargy, should prompt immediate attention to ensure the horse's safety and well-being.

In contrast, increased appetite might suggest the horse is feeling good and not experiencing heat stress, a calm demeanor typically indicates that the horse is relaxed and not stressed, and fast recovery after work generally indicates a healthy condition, as it suggests that the horse's heart rate and respiration return to baseline levels efficiently.