The Importance of Maintaining Adequate Hydration in the Equine Athlete

Nutrition and exercise are important in the maintenance and development of healthy muscular and skeletal systems. Deficiency or excess in either will cause or predispose these systems to disease.

Physical exertion of an equine athlete causes as much as a 10-20 fold increase in energy utilization, depending on the individual horse’s fitness level. Most of this energy is expelled as heat, which must be eliminated through evaporation of sweat. Fluid loss through sweating is elevated in extreme environmental conditions such as the summer months.

The greater the volume of sweat, the greater the loss of water and electrolytes. Under favorable climatic conditions, sweat loss can be up to 5-8L/hr. In hot or humid conditions, where sweating is less effective, fluid loss increases to 10-15L/hr.

Failure to replace these losses results in dehydration, electrolyte deficiencies, decreased circulation and, ultimately, decreased sweating, which can result in fatigue and less effective thermoregulation. The major electrolytes lost during physical exertion are sodium, potassium, chloride and calcium. Loss of sodium, potassium and chloride causes fatigue and muscle weakness, and will decrease the thirst response to dehydration – causing the horse to have little inclination drink or eat, further exacerbating the problem.

Dehydration and electrolyte deficits commonly occur in horses exhausted from prolonged or frequent physical exertion. In order to prevent this, water should be offered frequently with an attempt to replace the electrolytes that have been lost. This may be done by giving the horse 2 oz. (57g) of a mixture of three parts salt (1:1 mixture of sodium chloride and potassium chloride) plus one part calcium carbonate (limestone).

The body does not very efficiently store these electrolytes, so they should be given before, during and several times after exercise. Electrolytes may be supplemented in a variety of ways, but it should be noted that if they are added to water, plain non-supplemented water should also be available.

If electrolyte losses are small, little benefit is derived from electrolyte supplementation. Conversely, if moderate to severe electrolyte deficits do occur, they may lead to colic, muscular cramping, synchronous diaphragmatic flutter (“thumps”), hypocalcemic tetany, rhabdomyolysis and prolonged post-exercise fatigue. Affected animals appear obtunded and lethargic, often with little interest in food or water.

Exhaustion generally occurs as a result of whole-body deficits in energy, water and electrolytes. Many horses are willing to work to a point where they are too exhausted to go on and therefore should be monitored closely for an adequate balance of fluid loss versus intake and replacement.

For equine care and 24/7 emergency, call 360.568.3111.