The phrase dog days refers to the sultry days of summer. In the Northern Hemisphere, the dog days of summer are most commonly experienced in the months of July and August, which typically have the warmest summer temperatures.

A healthy sweating horse

The horse's physiological efficiency may then become compromised when excess activity, particularly during hot weather, leads to excess evaporation and resulting dehydration.
© 2017 by Cheryl Ann Quigley

The dog days of summer can have serious consequences for horses, especially when humidity is high, the temperatures are hot, and the horse has work to do, whether simple exercises or long trail rides.

Evaporation is the main way a horse gets rid of heat built up through activity. The horse's physiological efficiency may then become compromised when excess activity, particularly during warm weather, leads to excess evaporation and resulting dehydration.

Sweating at an acceptable level can occur only when a horse is fully hydrated and has plenty of fluids in the body to maintain bodily functions, as well as regulate temperature through evaporation off the skin surface.

Prolonged maximum exertion on humid days will cause the horse's body to become stressed, leading to a variety of physiological problems, including poor heart and respiratory responses, kidney impairment, muscle spasms, heart arrhythmias, gastrointestinal stasis, fatigue, and reduced muscle function.

Because water is also lost through the saliva it takes to soften food, through urine and feces, as well as through the moisture in the horse's breath, the animal needs to have access to plenty of cool, fresh water on hot summer days with most horses requiring a minimum of ten to twelve gallons of a day or more.

In addition to water, the horse's body requires electrolytes for biochemical reactions within the body to get nutrients in and waste products out. Electrolytes are responsible for nerves functioning properly and muscles contracting properly. If a horse sweats out these electrolytes in too large amounts, balance is not maintained, and the horse's ability to endure is greatly compromised.

Never riding or exercising a horse to the point of exhaustion is another way of preventing dehydration. Forcing a horse to be active in hot, humid weather almost insures dehydration and electrolyte imbalance.

Wise timing of exercise by taking advantage of cool periods during the day and making sure the horse has time to drink and has access to salt during the activity will keep the horse safe from the consequences of prolonged periods of dehydration.

4 ways to prevent dehydration in your horse:

• Check for signs of dehydration regularly, and don't wait until a horse looks dehydrated to administer electrolytes. Learn to perform skin pinch and mucous membrane testing and how to listen for gastric sounds to help determine when a horse is becoming dehydrated.
• Access to plenty of clean water with the opportunity to drink any time the horse is thirsty, plus monitoring how much the horse is drinking, will help keep the horse properly hydrated.
• Increase salt intake to stimulate a sweating horse to drink more. A 1,000 pound horse should be consuming about two ounces of salt per day, and salt should be available at all times.
• Feeding a well-formulated commercial ration intended for the level of activity of the horse will help prevent electrolyte imbalance and help enhance hydration.

If a horse becomes severely dehydrated, the introduction of warm water to the stomach by tube or intravenous rehydration may be necessary. Adding extra water to mash, and letting it sit for 10 minutes to permit expansion of the grain will also help with water intake.

The good news is that, given the opportunity to drink and the availability of sufficient fresh water, most horses will not suffer from dehydration and will make it through the dog days of summer without suffering serious consequences.