The effect of thermal environmental conditions on the health and performance of horses

Horses are adaptable to a wide range of environmental conditions and are found in climates where temperatures may fall as low as-40°C or rise as high as +40°C. Being a large mammal and thus having a low surface area to body mass ratio (~1:100; m 2:kg), the horse has a greater capacity to retain than dissipate heat. Whilst this is an advantage in cold climates, in hot or hot and humid climates this may render the horse at a disadvantage. For a large mammal, the horse also has a tremendous capacity to utilise oxygen for ATP regeneration. During exercise the predominant sites of ATP turnover and thus heat production are the locomotory muscles. If different compartmental temperatures are measured during exercise, the hierarchy is usually muscle (up to 46°C), blood (up to 45°C for pulmonary artery temperature), rectal (~42°C) and skin temperature (~40°C). As the rate of heat production is related to the rate of oxygen consumption, a high maximal oxygen uptake indicates that on a per kg basis the rate of heat production will also be high. For horses exercising at trot, the rate of heat storage, assuming no heat dissipation, would equate to an increase i