Feeling the heat

High temperatures increase the risk of overheating in active horses. Adam Jackson MRCVS explains equine thermoregulation, the risks and treatments

- Adam Jackson

EXERTIONAL heat illness (EHI) is a complex disease in which a horse is at significant risk, due to the fact that a horse has a high rate of heat production associated with its metabolism. To understand how this disease manifests and to develop preventative measures and treatments, it is important to understand thermoregulation in horses.

HOLDING STEADY

THERMOREGULATION allows the horse to maintain its body temperature despite continuous changes in the surrounding temperature, within certain limits. It is part of the greater process of homeostasis, which is a number of self-regulating processes the horse uses to maintain body stability in the face of changing external conditions. Homeostasis and thermoregulation are vital for the horse to maintain its internal environment to ensure its health – disruption of these processes leads to diseases.

The horse’s normal temperature range is 37.5°C to 38.5°C (99°F to 101°F). Hyperthermia is the condition in which the body temperature increases above normal due to the level of heat increasing faster than the body can reduce it. Hypothermia is the opposite – the body temperature decreases below normal levels as the body is losing heat faster than producing it. Both conditions are due to the malfunction of thermoregulatory and homeostatic control mechanisms.

During exercise, a horse converts stored chemical energy into mechanical energy when contracting various muscles in its body. However, this process is relatively inefficient because roughly 80% of the energy released from energy stores is lost as heat. The horse must have effective ways to dissipate this generated heat, otherwise the raised body temperatures may be life-threatening.

GENERATING HEAT