Why not – and what is needed?
When horses train and sweat, they lose sodium, potassium, and other electrolytes through sweat. These nutrients are easily overlooked, even though adequate access to clean water and salt is critically important for all animals, and especially for sport horses that sweat heavily. Electrolytes are essential for maintaining osmotic pressure, fluid balance, and the normal function of nerves and muscles. An electrolyte supplement is needed when a horse sweats heavily or for prolonged periods. During hard work, a horse can lose as much as 10–15 litres of fluid and up to 100 g of salt per hour. Low electrolyte levels reduce the volume of circulating blood in the veins, and the horse’s performance declines.
It is important to understand that horses differ from humans in their electrolyte needs. Horse sweat is hypertonic, meaning it contains a higher concentration of electrolytes than the fluid circulating in the body. Human sweat, by contrast, is hypotonic, meaning electrolyte concentrations are higher in the body than in sweat. Giving only water to a sweating horse merely dilutes the body’s electrolyte concentrations. For this reason, horses require electrolytes to maintain fluid balance and proper cellular function, both of which are essential for performance.
Under normal conditions, when a horse sweats only small amounts, plain salt is often sufficient to replace losses. As sweating increases, it becomes important to replace lost electrolytes with a proper electrolyte supplement that also contains potassium, sodium, and chloride, and possibly magnesium.
With sugar or without?
Many electrolyte products contain large amounts of sugar, but as a general rule, sugar does not belong in electrolytes. The use of sugar in equine electrolyte supplements originates from human studies suggesting that sodium is absorbed more efficiently together with glucose. Research conducted in horses shows that this same principle does not apply to horses. Sugar does not improve electrolyte absorption in horses and may, on the contrary, cause muscle problems. This is especially relevant in horses with insulin resistance or other metabolic disorders.
Horses do not need extra sugar, particularly when dehydrated. Horses convert digestible fibre into glucose, glycogen, and fat with the help of beneficial gut microbes. Sugar is not required for electrolyte absorption, and it may excessively dilute more valuable and necessary ingredients.
The most important components of electrolytes are sodium, chloride, and potassium. Other components may include calcium, phosphorus, magnesium, copper, iron, manganese, and zinc.
A small amount of sugar in an electrolyte product can be acceptable, as long as it contains the essential electrolytes and minerals. Small amounts of sugar do not significantly affect absorption. Sugar may improve palatability, but it offers no other real benefit. Palatability can also be improved using healthier alternatives than sugar. Large amounts of sugar reduce the proportion of electrolytes consumed and are not beneficial for electrolyte replacement. It is therefore worth checking both the sugar and electrolyte content of any electrolyte product.
What do electrolytes actually do?
So what exactly are electrolytes, and what do they do? When dissolved in water, electrolytes dissociate into charged ions, creating an electrochemical current. This current acts as a catalyst for many bodily processes in the horse, including muscle contraction, nutrient absorption, nervous system function, acid–base balance, and fluid regulation. Electrolytes direct water intake to the cells, organs, and tissues that need it most.
Sweat consists of both water and electrolytes. When horses sweat, they lose not only water but also valuable minerals that are responsible for many biochemical processes in the body. Replacing lost electrolytes is therefore crucial for the horse’s health. The more a horse sweats, the faster it needs replenishment.
Electrolyte imbalance and deficiencies cause dehydration and can affect the horse in many ways, ranging from loss of energy and muscle tremors to weakness, instability, and in severe cases even death. For this reason, it is important to recognise when electrolyte supplementation is necessary.
Electrolytes play key roles throughout the horse’s body. Their electrochemical processes help regulate heart rate, muscle contraction, nerve impulse transmission, and digestion. They also help move fluids into and out of cells and promote nutrient absorption. Without electrolytes, the horse’s body cannot retain or utilise water effectively.
What and how much?
A lightly sweating horse needs only salt to replenish sodium and chloride levels that are insufficient in the diet. Potassium supplementation is usually unnecessary, as hay and pasture grass contain plenty of potassium. A horse that trains actively or works in extremely hot conditions and sweats heavily requires a dedicated electrolyte supplement. In such cases, salt alone is not enough.
Horses naturally lose electrolytes through sweat, urine, and manure, but they also obtain them—especially potassium—from grass, hay, and/or feed. Sodium and chloride are exceptions and must always be provided in the form of added salt in the daily ration (5–10 g/100 kg body weight/day).
The key is balance. Horses that sweat for prolonged periods need additional electrolytes, because large amounts of sodium, potassium, and chloride are lost through sweat. Potassium loss is approximately half that of sodium, while chloride loss is about twice that of sodium.
Sources:
- Lindinger M.I. (2022) Oral electrolyte and water supplementation in horses. Vet Sci. 9, 626
- Waller A.P. & Lindinger M.I. (2023) Tracing acid-base variables in exercising horses: effects of pre-loading oral electrolytes. Animals. 13, 73
- Zeyner A. et al. (2014) Scoring of sweat losses in exercised horses – a pilot study. J. Anim Physiol Anim Nutr. 98(2):246–250
- Pagan, J. (1998). Electrolytes and the Performance Horse. Advances in Equine Nutrition. Nottingham University Press
- McCutcheon, L.J. & Geor, R.J. (1998). Sweating. Fluid and ion losses and replacement. Vet Clin North Am Equine Pract. 14(1):75–95
- Jansson, A. & Dahlborn, K. (1999). Effects of feeding frequency and voluntary salt intake on fluid and electrolyte regulation in athletic horses. Journal of Applied Physiology
- Judd, B. (2016). Differences in horse sweat
