For heat dissipation and body cooling, a horse trotting at 11.2 mph loses about 3.3 gallons of sweat per hour under moderate conditions. The salts/electrolytes sodium, potassium, chloride, magnesium and calcium are also lost with this loss of fluid. These electrolytes are responsible for the transfer of water through cell membranes, for nerves to fire and muscles to contract. Large losses of electrolytes can result in several neuromuscular and systemic disturbances including muscle cramping, tying up, synchronous diaphragmatic flutter (thumps) and systemic alkalosis.
Our goal as the equine caretaker is to prevent electrolyte imbalance and dehydration in the performance/stressed horse thru proper fluid and electrolyte replacement. Balance can greatly prolong reaching the point of fatigue and also decrease recovery time.
If you're feeding a well formulated commercial ration intended for a performance horse, the chances are good that they've met the electrolyte needs of the lightly to moderately worked horse, under most conditions (always make plain salt available). Electrolyte availability can become a problem when the rate of loss exceeds the rate of replacement. If the horse sweats for a prolonged period of time, due to extreme weather conditions (high humidity, high heat), prolonged exercise (endurance type work), heavily worked/trained horses (race horses in training) or stressed horses (transporting), electrolyte needs will not always be met through their feed. For these horses, electrolyte supplementation becomes necessary to maintain body functions at an optimum level and to increase water intake preventing dehydration. Electrolytes should not be given to a horse that is already dehydrated, except under the supervision of a veterinarian.
Horses do not "store" sodium, potassium or chloride. Adding daily electrolyte supplementation would not be necessary, when feeding a balanced feeding program, unless the horse is being worked/trained hard daily and losing a large amount of sweat. When preparing for an event, choose an electrolyte formula that is palatable/acceptable to your horse, and don't wait until the day of the competition to find out. Use caution if adding electrolytes to water due to the possibility of decreased water consumption.
There are lots of opinions about appropriate administration schedules and dose rates. Follow the instructions per the brand that you choose. Learn and adjust to your horses specific needs and weather conditions. Train your horse to the level needed for the event. Increased electrolytes will not replace proper conditioning.
Electrolytes containing bicarbonate are formulated for horses with diarrhea. These can be harmful when used as an electrolyte supplement for stress and exercise.
Feeding electrolytes without proper water consumption will cause water to be absorbed from the bloodstream into the intestine, resulting in greater dehydration. From a non-working to a heavy working saddle horse, the water intake can increase 7 ? 10 gallons/day. Check for signs of dehydration regularly and don't wait until your horse looks dehydrated to administer electrolytes. Learn to perform skin pinch, capillary and jugular refill and mucous membrane testing as well as listening for gut sounds. Continue with electrolyte supplementation when the event is completed to aid in recovery if necessary.