As the summer heats up, we may not be the only ones that seek the cooling waters of our pools as our horses suffer too during hot weather.
What is the temperature that is most comfortable for our horses? Described as the thermoneutral zone (TNZ), the ambient temperature where the horse is most comfortable is estimated between 30 o to 75o F in still air (Stull, 1998). It is this temperature range that promotes maximum performance and provides the least amount of stress for the horse. Within this thermoneutral zone, the horse does not have to change metabolic heat production to maintain a constant core body temperature.
The upper critical temperature (UCT), approximately 75o to 90o F, is reached when the horse cannot dissipate enough metabolic heat to the environment to maintain homeothermy or maintain his body temperature at a constant level. Humidity is a major factor in the determination of the UCT as the horse dissipates heat through respiration and sweating mechanisms. The body temperature of horses is influenced by the ambient temperature, wind, sunlight, precipitation and relative humidity. Also keep in mind that horse’s produce a tremendous amount of heat during exercise and the rate of that heat production is directly related to the work effort, for example, the faster the horse runs, the greater the rate of heat production. As well, factors such as steep hills, difficult footing and the weight the horse carries (rider and tack) all increase the amount of effort level and will increase the rate of heat production.
There are a few formulas people use to calculate the heat index to see whether it makes sense to go out for a ride. One such formula is to take the outside temperature in Fahrenheit and add the relative humidity. For example, outside temperature of 50o F and humidity factor of 60% which would equal 110. If your total is below 120, you can ride without stress on your horse. If the total is between 130 and 150, the horse will sweat and you will need to pay attention to his water intake, but your horse should be able to maintain a reasonable core temperature. However, if the total is between 150 and 180, then stress on your horse is very likely and if the total is over 180, don’t even think about riding!
Feeding management is also affected by the temperature. Some horses will go off feed if they get too hot. Also remember that the digestion of feed results in the generation of body heat with some feeds generating more heat than others. Adding fat to the diet will increase the calories in the feed without increasing the volume of feed and fat burns cooler in the body than protein or carbohydrates. Feed only as much protein as the horse needs in order to reduce the feed heat load. Also feeding grass forages will decrease the metabolic heat generated as compared to feeding legume forage. But most importantly, is to provide plenty of fresh water to your horses as the hot temperatures will increase water consumption.
Overweight horses will have a harder time dealing with the heat with the added body fat which acts as insulation trapping body heat it makes it more difficult for the horse to cool off. Working an overweight horse in the heat is an excellent way to end up with a sick animal!
Happy riding, Larissa