Hot and humid summertime weather can appear suddenly after a prolonged cool spring in Illinois, so horse owners should be prepared to adjust management procedures as the weather changes.
Horses, ponies and other equids should have access to water at all times as summer approaches. Horses are very good at dissipating excess body heat through sweating, but sweating can quickly deplete important bodily fluids if horses cannot drink enough water to maintain a neutral fluid balance.
Horses will drink much more water during hot and humid weather compared to when weather is cool with low relative humidity. Pay attention to refilling water buckets and keeping automatic waterers clean, to ensure adequate drinking and be sure that group-housed horses have multiple water sources so that more timid individuals are not chased away from water by the more dominant horses.
Resist the idea that a hot and thirsty horse that has been exercising should be given water sparingly. If the horse is hot and thirsty, then it needs water, so let him drink as much as he wants, with short breaks from large swallows of water, so that the horse recognizes when he is satisfied.
Horses lose more than just water when they sweat. They also lose electrolytes including sodium, chloride, potassium, magnesium and calcium. At a bare minimum, horses should have free access to trace-mineralized salt in either loose or block form.
If a horse is competing and exercising regularly during hot and humid weather, it may be necessary to provide additional electrolytes designed to be dissolved in the water, or supplied directly into the horse’s mouth as a paste. Research has found that supplementing electrolytes encourages horses to drink more, on the average.
However, some horses are finicky about drinking electrolyte-supplemented water, so plain water should also be provided if there is any reluctance to drink the electrolyte-supplemented water. Inadequate or imbalanced electrolyte concentrations in body fluids can result in dysfunction of muscle contraction, breathing and heart function.
Horses in frequent work or competition during hot and humid weather are particularly prone to overheating. In addition to the recommendation to fluid-load as much as possible through encouraging horses to drink, horse owners should use all available modes of heat exchange to keep horses cool.
Avoiding work during the hottest hours of the day is a common-sense practice that is often overlooked or ignored due to scheduling difficulties. Keeping horses in the shade, which minimizes radiant heat gain from sunlight, is something that should be done routinely, but shade may be in short supply in many venues.
Horse owners should use fans to move air past the horse’s body, which will increase convective heat loss. Combining fluid loading and air movement from fans will accomplish two things.
First, more water will be available to produce sweat. Second, the sweat is then evaporated more rapidly due to the air movement. Therefore, convection and evaporative cooling work together to more efficiently cool the horse.
Finally, do not overlook conductive cooling of the horse by liberally applying cold water to the entire horse, especially following hard work in the heat and humidity.
The idea that horses may be harmed in some way by pouring cold, even ice-cold water over their overheated bodies has been thoroughly disproven by research conducted at the 1996 Olympic Games in Atlanta, which was one of the hottest environments for equestrian competition in recent history.
Horses bathed in water from a slurry of ice and water, cooled down more rapidly and had no signs of tying-up, based on blood levels of AST and CK enzyme concentrations.
Using the strategies of fluid-loading in anticipation of evaporative cooling, encouraging heat loss using conduction, convection and minimizing radiant heat gain from sunlight can help to avoid heat stroke in horses, when body temperature can reach a dangerous level of 108 degrees or more.
Horse owners should recognize that environmental conditions could change rapidly and be ready to adapt management of horses as hot and humid conditions begin to occur this time of year.
Kevin H. Kline, is a professor, University of Illinois, Department of Animal Sciences.