Your Horse: Heat Stress and Hydration

times more heat per unit volume than air. Because of this, water can cool the body four times faster than using air of the same temperature. Contrary to popular belief that ice-cold water will cause vasoconstriction and actually slow down cooling, there is little evidence to support this. Exercising individuals who are overheated do not show the same vasoconstriction response to cold water as those who are at an ideal body temperature, and bringing the temperature down rapidly in an overheated horse is critical to avoiding serious heat injury.

Another essential strategy to avoid heat injury is maintaining good hydration, ideally through provision of water and electrolytes. Sedentary horses living in a moderate climate drink about five litres per 100 kg of body weight per day. When living in a cold climate, there is evidence that they prefer water at “room temperature” (approximately 20 degrees C) and tend to drink quite a bit less when the water is close to the freezing mark (around two degrees C). In the heat, however, they don’t seem to mind either way. Water demand can increase by ten times when horses are exercising in hot, humid conditions, and sometimes just offering water may not be enough. A dehydrated horse does not have the same thirst response as a human does, so including electrolytes in the water that is offered before and after exercise can help hold the water in the horse’s body (rather than being excreted by the kidneys).

What does this mean for your horse? Make sure your horse has access to clean, fresh water at all times. Electrolytes can be added to the water to improve hydration during exercise in hot, humid conditions. When exercising in the heat, consider working him or her during the cooler parts of the day (before 11am or after 6pm). Work horses on grass rather than sand when possible, as sand reflects solar radiation more than grass, and have shaded areas available. Use ice-cold water to cool down hot horses as rapidly as possible. And once your horse is nice and cool you might want to take a dip in a cold water trough yourself!