Recent studies confirm what some Veterinarians have been saying for quite some time – we may have been taught the wrong approach to cool a hot horse. This time of year, many horse owners are taking additional measures to prevent their horses from overheating as well as implementing an effective routine to cool their horses down after exercise or a particularly hot day. Most horse owners have been taught to hose the horse down with water and, most importantly, scrap off the water. The theory behind scraping the water off is related to the idea that water on a horse acts as an insulator and actually makes the horse warmer – this is not true.
So why does a horse feel warmer to the touch when you are hosing it off with water? This occurs when the scientific process of “conductive transfer of heat” takes place between the water and the horse. When there are two “bodies” in direct contact, in this case, the water and the horse, heat passes from the hotter body to the cooler body until they are at the same temperature. Thus, heat is transferred from the warmer horse to the cooler water because there is a temperature difference. The larger the difference in temperature between the horse and the water, the faster the heat is transferred.
Will the water sitting on the horse make it heat back up? No, it will not. This is because the water on the horse is not acting as an insulator but rather helping to further cool the horse by the process of evaporation. Water is a much better conductor of heat than air. Evaporation of water uses up energy and cools the surface on which the water sits. This means a wet horse will stay cooler than a dry one. Scraping the water off is not harmful but it is less effective at cooling the horse. What is the best method for cooling a very hot horse? The best method for maximum cooling is to combine the benefits of both conductive transfer of heat and evaporation. Cool the horse through a continuous application of cold water over the entire body. Once the horse is sufficiently cooled, leave the water on the horse to further cool it through evaporation.
A Comparison of Five Cooling Methods in Hot and Humid Environments in Thoroughbred Horses. Journal of Equine Veterinary Science, Volume 91. August 2020.