Mostert H J, Lund R J, Guthrie A J, Cilliers P J
Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, South Africa.
Equine Vet J Suppl. 1996 Jul(22):7-15. doi: 10.1111/j.2042-3306.1996.tb05026.x.
A theoretical integrative model was developed to determine the heat balance of horses working in a given environment. This model included the following parameters: metabolic heat gain, solar heat gain, evaporative heat loss due to sweating, respiratory tract heat loss, radiation from the body and heat gain or loss due to convection and conduction. The model developed in this study includes an unique approach for estimating heat loss via evaporation of sweat from the animal's skin surface. Previous studies modelling evaporative heat dissipation were based on the volume of sweat loss. While it is known that the ambient conditions affect evaporation rate, these effects have not been adequately described. The present model assumes the horse's skin surface is adequately represented by a body of water and it describes the interaction of that water body with the atmosphere. It is assumed that sweat has thermodynamic characteristics equivalent to distilled water. Sweat, however, has high electrolyte and protein concentrations and anecdotal evidence has shown that the thermodynamic characteristics may be significantly affected. Further research is, therefore, required to confirm these characteristics for equine sweat. The model describes all factors known to affect the thermal balance of the horse working in a given environment. The relative significance of the various variables on the whole integrative model has been illustrated. The effect of ambient temperature and humidity on the evaporative heat loss, the most significant and critical avenue of heat dissipation, is defined and quantified. The model illustrates clearly how increasing relative humidity limits evaporative heat loss, which can be further compromised when horses exercise on treadmills with no air movement.
开发了一个理论综合模型来确定在特定环境中工作的马匹的热平衡。该模型包括以下参数：代谢产热、太阳得热、出汗引起的蒸发散热、呼吸道散热、身体辐射以及对流和传导引起的热得失。本研究中开发的模型包括一种独特的方法来估计动物皮肤表面汗液蒸发产生的散热。先前模拟蒸发散热的研究是基于出汗量。虽然已知环境条件会影响蒸发速率，但这些影响尚未得到充分描述。当前模型假设马匹的皮肤表面可以用一个水体来充分代表，并描述了该水体与大气的相互作用。假设汗液具有与蒸馏水等效的热力学特性。然而，汗液具有高电解质和蛋白质浓度，轶事证据表明其热力学特性可能会受到显著影响。因此，需要进一步研究来确定马汗的这些特性。该模型描述了所有已知会影响在特定环境中工作的马匹热平衡的因素。阐述了各种变量对整个综合模型的相对重要性。定义并量化了环境温度和湿度对蒸发散热（最重要且关键的散热途径）的影响。该模型清楚地说明了相对湿度增加如何限制蒸发散热，当马匹在没有空气流动的跑步机上运动时，这种情况可能会进一步恶化。
