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. | Photo: iStock

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