Like humans, a horse’s main cooling mechanism is sweating. The evaporation of sweat helps cool the skin and lower body temperature. The increase in humidity during the summer can reduce the evaporation of sweat, meaning your horse will overheat more quickly. If possible, work your horse in the cool of the morning and evening and regularly check the level of water in your horse’s stock tank. If you have to work or show your horse during the heat of the day, make sure that it has regular access to water since a dehydrated horse will not be able to produce enough sweat to keep itself cool.
Always have a water bucket and hose on hand when showing horses. Be careful not to give a hot horse cold water and then let it stand. Follow the “six sips and walk” rule. Loss of fluids can cause colic in horses, and dehydration and heat stroke can be deadly. If your horse stops sweating, immediate attention is required.
Another concern related to dehydration is loss of electrolytes. Electrolytes are electrically charged mineral salts like sodium, potassium, and chloride that help regulate nerve and muscle function. A loss in electrolytes can lead to nervousness, muscles cramps, and even heart problems. If your horse works at light to moderate levels, providing it a nutritionally balanced food, good hay, adequate water, and a salt block should enable your horse to replenish everything lost through sweating.
A horse working at high levels may require as much as six ounces of salt a day and it probably will not eat this much from a salt block. Electrolyte supplements are a good choice for a horse being worked hard; however, supplements should be used with care since too much will actually dehydrate a horse even more. Along with plenty of water, provide an electrolyte supplement the day before, the day of, and the day after an event in which your horse works and sweats excessively. If your horse starts urinating more than normal it could be a sign that it has been allowed too much of a supplement and is trying to rid its system of excess salt.
Finally, changing your horse’s diet during the summer can go far in keeping it cool. A horse’s diet is very high in fiber, which requires a lot of energy to digest. Digestion produces heat so switching to a food source easier to digest will help keep your horse from overheating. Also, feeding several small amounts throughout the day rather than two large meals may help even out body heat produced by digestion.
Hay that is a grass and legume mix with a fine, soft texture will be easier for your horse to digest than woodier hay. Adding a fat feed or corn oil into your horse’s diet will enable you to provide the needed nutrition while feeding less volume, and so lower the amount of heat produced by digestion. Adding fat may also help increase endurance while reducing fluid loss. However, avoid high levels of protein as the excess of nitrogen in a high protein diet can increase fluid loss due to higher urine output.