The changing of the seasons is a much anticipated event; especially for horse enthusiasts, when the warmer weather means bringing out the tack and brushing off the winter dust for horse and rider.  The spring, summer and early fall months may mean more competitions, shows, or sojourns to the countryside, and those things make the matter of adequate hydration more important than ever.  A horse should always have clear and unrestricted access to clean water.  Warm temperatures and humid weather can change and effect the way horses are able to cool themselves. 

When a horse works, it sweats.  Sweating is a form of thermoregulation by which horses and other animals keep their body temperatures within certain boundaries, even when the surrounding temperature is very different.  The process of sweating works by decreasing core temperature while evaporation reduces surface temperature.  The type and degree of exercise  determines how much an animal sweats.  Only horses and humans sweat profusely to cool the body down.  The sweat composition in horses contains a much larger amount of electrolytes than in humans.  Electrolytes are lost in the sweat.  Excessive sweat loss can cause an electrolyte imbalance, which in turn can rapidly lead to premature muscle fatigue, reduced stamina, muscle cramps and poor post-exercise recovery if not corrected.  Horses lose about 3 times more sodium and up to 10 times more potassium in sweat than humans.  The electrolytes lost every day in work also include magnesium, calcium, chlorides, sulphates, phosphates and bicarbonates.  These electrolytes are lost in the form sweat, urine and feces.

Sodium and chloride are the two major electrolytes lost in sweat.  Normal salt does not replace the other essential electrolytes, nor will it help buffer the acidosis caused during hard work.  Sodium helps balance the body’s water levels and maintains blood pressure.  Chloride helps maintain the balance of acids and bases.  Calcium (in addition to building bones & teeth) contributes to normal heart function, nerves, muscle and blood clotting.  The loss of both potassium and sodium in sweat acts to rapidly decrease thirst and appetite, and this actually increases dehydration because the horse will not eat or drink sufficient food and water to replace the electrolyte losses unless supplements are used regularly to replace the deficit.  Any athlete will tell you how tired they feel and how their performance drops rapidly during and after prolonged sweating.  This is partly because the potassium loss decreases muscles’ strength, tone, and ability to contract.  Potassium helps balance the fluid inside the cells and is vital for optimum muscle, heart and kidney function.  It’s the same way for our equine friends!

Dehydration has many causes, including the failure of the owner to provide clean water, sweating/heat exhaustion, fever, and prolonged diarrhea to name a few.  Even a lactating mare has an increased need for water consumption.  Horses can go up to 25 days on a diet of water only, but can only survive 5-6 days without it.  After a few days without water, the animal stops eating and will die shortly after.  The lack of water may result in: loss of performance, muscle damage, reduced kidney function/renal failure, laminitis, tying up, coma and/or death.   Even when the animals have the access to water, any sort of contamination (such as a dead bird) in their watering hole or trough will have them refusing to drink.  Make sure to check the containers for any foreign contaminants.  A good rule of thumb is:  if you wouldn’t drink it, don’t expect them to.

Equine dehydration can have numerous other causes such as endotoxemia, anaphylactic shock, sickness, and severe burns.  A horse is comprised of 65 to 70% water; their brain is 85% water; the muscles, 75%, and the bones are 30% water-based.  If you were to drain all the water out of a 1,000 lb horse, 70 gallons would have been removed, leaving the horse weighing an approximate 440lbs.  Just as water is vital to human survival, it’s even more so to the equine.  Dehydration can cause permanent damage to organs and also prevents nutrients from being absorbed as they should and puts the horse at risk for colic, the number one killer in horses.  Although the symptoms of colic can often be helped through the use of various probiotic powders and supplements, it can also be a very serious problem.

With the waning of winter turning over to spring and summer, humans and animals alike are looking forward to the warmer temperatures and fairer weather of the upcoming months.  The new season requires a different sort of hydration program and balance than what was done during the colder months.  When the temperatures are in the 80s or 90s, the risk for dehydration and electrolyte loss dually increases, especially during exercise or competition.

Please take the time to ensure that your animal has plenty of access to clean water.  If possible, take breaks often in the shade.  Ben Franklin may well have had horses in mind when he said “An ounce of prevention is worth a pound of cure.”