Once you know the basics, it’s not that difficult to supplement electrolytes correctly but many people don’t know how and it’s taking more of a toll than is realized.
Even mild dehydration can have a major effect on performance
Electrolytes are minerals that exist in the body in their free, ionized form – i.e. carrying an electrical charge. Cations like calcium, potassium and sodium have positive charges. Anions like chloride, bicarbonate and sulfate are negative.
Much like in a battery, movement of electrolytes makes excitatory activity possible, such as muscles contracting, nerves firing and the heart beating. Electrolyte concentrations and gradients also allow the body to hold normal amounts of water (hydration) and the kidney to adjust the concentration of urine.
Sweat is a major avenue of loss for sodium, potassium, chloride and to a lesser extent calcium and magnesium but it’s not the only avenue.
The horse also has daily endogenous losses in urine, sloughed cells, mucus and the digestive tract. Those losses must be met by the diet on a daily basis. Failure to do that is one major reason why even horses getting electrolyte supplements are often deficient and dehydrated. These baseline daily losses (not including sweat) are 10 grams sodium, potassium 25 grams, chloride 40 grams for a 500 kg horse.
Hay takes care of baseline potassium needs at an intake as low as 1% of body weight. Chloride requires closer to 2% of body weight but some will also come from salt (sodium chloride). Sodium requirements have to come from salt. The baseline requirement for sodium can be met by approximately 2 oz of salt in hot weather = one stall size salt lick per month. Salt may also come from supplements, commercial feeds or be added to feed or sprinkled on hay.
Once the baseline requirements are adequately met you can work on replacing sweat losses. At low rates of sweating, the horse will average losses of approximately 10 grams of sodium, 5 grams of potassium and 20 grams of chloride per hour. That’s a ratio of 2:1:4 for sodium, potassium and chloride. Check to see that your replacement supplement has those correct ratios or you may be making things worse. Low levels of calcium and magnesium (typically 200 to 300 mg/hourly dose) may also be used. Magnesium losses in particular may be important since many diets are borderline to deficient already.
To determine dosage, calculate average sweat losses as above then look at the amount per dose on the label. For example, an hour of light sweating needs 10 grams of sodium so if the product provides 5 grams (same as 5,000 mg) per dose you need 2 doses. Do not rely on manufacturer’s suggestions alone.
Horses already showing signs of electrolyte deficiency and dehydration such as weakness, muscle trembling, thumps or poor gut motility may also benefit from use of a paste that has a higher amount of potassium as well as additional magnesium and calcium. Potassium in blood is depleted quicker than sodium despite being lower in sweat. This is because sodium is pulled from tissues to replace blood sodium and also because the kidney will substitute potassium for sodium in urine when blood sodium is low.
It isn’t particularly difficult to figure out how much electrolyte supplementation your horse needs. Just takes a few minutes. It’s time very well spent and you will quickly see how much easier and better your horse performs in hot weather.
Eleanor Kellon, VMD