Salt Intake, Lethargy, and Weight Loss: What's the Connection?

Q. Recently my Thoroughbred has been lethargic and has lost weight. I live in Arizona, and it has been well over 100 degrees for the past month, sometimes as high as 116° F. He tends to lose weight in the summer when it’s hot; however, he has not been lethargic in previous summers. He eats a combination of alfalfa and Bermuda hay. Someone mentioned that his weight loss and lethargy might be due to a lack of salt. He does sweat very heavily on hot days. Often when I arrive at the barn in the evening he has dried salt in his hair over his back. Could a lack of salt cause weight loss and lethargy?

A. Maintaining a horse’s weight in very hot climates can be just as much of a challenge in very cold climates.

Common salt is a combination of sodium and chloride (note that “lite” salt is potassium chloride), with about 61% being chloride and 39% sodium. Forages are typically low in sodium and chloride, and commercial feeds tend to only add about 0.5% sodium chloride, which isn’t enough to meet the horse’s daily requirement. If horses don’t have adequate access to these minerals, they can become deficient. This can be especially true if horses are sweating heavily, because horse sweat contains relatively high concentrations of these electrolytes.

Typically, a salt deficiency takes weeks or months to develop, because horses are fairly good at regulating their sodium and chloride levels. If, however, a deficiency exists and it’s not addressed, weight loss is possible due to reduced feed intake. This might develop into anorexia in severe cases. Weakness can also develop as a clinical sign, in addition to dehydration. Horses that are worked while suffering from a deficiency will fatigue more quickly, and this could be part of the lethargy your horse is experiencing.

Salt Intake, Lethargy, and Weight Loss: What’s the Link?

I’m not sure whether you provide your horse with a salt block, but I recommend horses have access to salt at all times, because they’re good at regulating their sodium chloride intake when salt is available. However, they might not consume enough from a block, because blocks were developed for cattle that have rough tongues, and horses have smooth tongues. Therefore, adding salt to their daily feed is a good idea, so you can know they’ve consumed their minimum requirement for maintenance.

Per the National Research Council (NRC), the maintenance level of sodium chloride for an adult horse is about 25 grams a day or just under an ounce (2 tablespoons). Keep in mind this only meets their needs on a cool day when doing no forced exercise. On hot days or when working harder, horses require higher sodium levels better met by feeding a well-formulated electrolyte, which will likely be more palatable than plain salt. A good electrolyte needs to have salt or chloride as the first ingredient—dextrose or sugar—and should be formulated to replace sweat losses.

If you want to see if a salt deficiency is your horse’s issue, gradually increase his salt intake. Provide 24-hour access to a salt block or loose salt and build up to giving 2 tablespoons a day of salt. If this doesn’t result in an improvement in your horse’s lethargy, I recommend having the veterinarian examine your horse to rule out other causes of lethargy and weight loss.