About Horses, Exercising & Rehydration.

Q: One dangerous myth I hear is the one that says hot, sweaty horses shouldn’t drink cold water because it will cause them to colic, founder or tie up. Often I see people waiting until the horse is literally begging for water, and even then the rider is hesitant to let him drink for fear he will colic. Would you please assure owners (and me) that it’s OK to let hot horses drink?

A: The notion that a hot, recently exercised horse needs to cool down before drinking water is indeed a myth—unfortunately, one of many about horses and colic.

In a series of studies, scientists at the Michigan State University Veterinary Medical Center have been investigating the various factors that influence the voluntary water intake of horses after prolonged exercise.

They made horses dehydrated in the first study by giving them exercise on a treadmill equivalent to a 45km endurance ride. In two other studies the also gave a potent diuretic to increase the degree of dehydration.

Next- researchers investigated whether restricting the water intake immediately after exercise affected total water intake. Traditional advice has been to limit the intake of water immediately after exercise. This was because of the perceived risk of causing colic or laminitis. However researchers found that this fear is ungrounded. Horses given free access to fluid immediately after exercise had no greater incidence to these problems. And in fact, horses tended to limit the fluid intake to the size of their stomachs ( about 10 liters). On the other hand, restricting the amount of water in the first five minutes after exercise did not adversely affect the overall recovery from dehydration.

In the second part of the study, the researchers compared the effect of giving either plain water or two different concentrations of salt solution as the initial rehydration fluid. This was then followed by free access to plain water from twenty minutes after the exercise period, and recorded total fluid intake in the first hour after exercise. They found that using water as the initial rehydration fluid is less effective than either of the salt-water solutions. They suggest that this may be because the plain water dilutes the salt concentration in the blood, reducing the stimulus for thirst.

Finally, they assessed whether the temperature of the rehydration fluid affected the total fluid intake. Fluid intake was greater when the fluid was at room temperature rather than cooled, or at near body temperature.

As a result of their findings, they recommend:

  • Allow free access to fluids straight after exercise
  • Offer salt water at concentrations up to 0.9% salt as the initial rehydration liquid, after that- change to plain water.
  • Give fluids at ambient temperature. There is no benefit using cold fluids or those at body temperature.

They also point out that the body fluid and electrolyte depletion can persist for several days after prolonged exercise. Several meals may be required to fully replenish electrolytes lost in sweat after prolonged exercise.