Do you know how to supplement electrolytes properly to meet your horse's needs?
Probably not. If you are relying on the manufacturer's recommendations to get it right, the odds are even worse.
Electrolytes are minerals that are free within the blood and body in an ionized state - carrying an electrical charge. The major ones are sodium, potassium, chloride, and bicarbonate with much lower levels of calcium, magnesium, phosphorus, and others.
There are baseline losses of electrolytes into the urine and/or manure that occur on a daily basis year-round. This loss should be the foundation for supplementation. Sodium is in the shortest supply in the basic diet, foll0wed by chloride, so salt (sodium chloride) is a daily need to the tune of 10 grams of sodium, the equivalent of about 1 oz of salt, for a 500 kg/1100 pound horse. If you are relying on a stall brick salt lick to meet this need, the horse would have to go through a brick about every 2 months.
Some health problems like colic, kidney disease, and diarrhea, can change electrolyte requirements but the most common reason for increased losses is sweating. Large amounts of sodium, potassium, and chloride are lost. Potassium loss is about half as much as sodium; chloride is twice as much as sodium.
At low levels of sweating a horse will lose a little over 10 grams of sodium/hour. Low-level sweating would be along the neck, between hind legs, and under the saddle. At the highest level of sweating, the body totally wet and dripping, it can be over 40 grams of sodium/hour. Since every 10 grams is the rough equivalent of 1 oz of salt we're talking between 1 oz and a half a cup of salt lost in an hour of sweating.
The major consequences of electrolyte loss include impaired performance/endurance, dehydration, muscular weakness, deranged neurological function, and impaired intestinal function.
Since hay and pasture have generous levels of potassium if your horse is only sweating lightly and working 1 to 2 hours you can get away with supplementing only plain salt at an extra 1 oz per hour of work. Be sure to add this directly to food or a separate electrolyte water bucket and also make sure the baseline 1 oz/day of salt is also being ingested.
If sweating heavier or working longer than 2 hours you should use an electrolyte supplement that matches sweat losses so a ratio of roughly 2:1:4 for sodium:potassium:chloride. When you find an appropriate product, calculate the amount to feed based on sodium loss and everything else will fall in line if the ratio is correct.
Hodi is working 3 hours/day at a moderate rate of sweating. With 10 grams of sodium/hour being the lightest and 40 grams the highest sweat losses, he is estimated to be losing 20 grams of sodium/hour so 60 grams total for the day in sweat. Hodi's electrolyte supplement has 11 grams sodium, 21 grams chloride, and 5 grams potassium per serving so the ratio is good. To replace the 60 grams of sodium lost, with accompanying chloride and potassium, he would need 60 [total g lost]/11 [g per serving] = 5.45 servings.
Sweat also contains much smaller amounts of protein and other minerals - loss in an hour of light sweating of 2.5 g protein, 0.3 g calcium, 0.1 g magnesium, and trace minerals. These losses are not likely to be of nutritional significance except with very heavy sweating for prolonged periods.
Figuring out your horse's electrolyte needs isn't rocket science and only takes a few minutes. Meet baseline needs then add sweat losses. You may be amazed at how much more energy and vigor your horse has.