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Timing for Electrolytes

Electrolytes are a class of minerals that are integral to function of many organ systems, including but not limited to: muscles, heart, digestion, nervous system, and kidneys.  Further, electrolyte balance is entangled with hydration status, so disruptions in either electrolytes or hydration can lead to fatigue, muscle twitching, heart arrhythmias, respiratory distress, abnormal GI tract motility, poor performance, etc. (Lindinger, 2005). 

As sodium is naturally low in equine diets and horses are unlikely to meet their sodium needs by diet alone, and electrolytes are lost at higher rates for horses in training or sweat-inducing temperatures (National Research Council, 2007), electrolytes in some form should be supplemented at all times in some way for basically every horse.  Repeatedly, studies have shown the significant imbalances in electrolytes and hydration that occur as a result of exercise in non-supplemented horses (Düsterdieck et al., 1999; Hyyppä et al., 1996; Kronfeld, 2011; Robert et al., 2010), putting the health and performance of horses at risk, and particularly when exercise bouts are repeated day-to-day, since imbalances worsen as time goes on (Assenza et al., 2014; Hoyt et al., 1995) and the longer horses sweat (McConaghy et al., 1995).  In endurance sports particularly, electrolyte imbalances have been correlated with a higher chance of not being able to complete a race successfully (Muñoz et al., 2010).

Horses at maintenance or low work or cool temperatures can best meet their basic needs with the addition of around 2 tablespoons table salt (for the average size horse) or top dressed commercial supplements, as salt blocks have been shown to be insufficient to stimulate voluntary intake of enough salt to meet daily needs and stimulate drinking (Gordon and Jarina, 2013). 

Horses in at least moderate exercise or hot climates will need to receive higher levels and more variety of electrolytes in their supplement (such as combinations of sodium, chloride, calcium, magnesium, and potassium to match ratios lost in sweat).  For these horses, commercially designed, palatable supplements that can be dosed for their weight and work load are most appropriate to ensure they meet the horse’s needs.  Even with regular daily supplementation, it is possible with particularly intense exercise, consecutive days of exercise, or endurance sports, additional dosing of electrolytes may be needed during and/or after competition to quickly and efficiently replace lost electrolytes and to help maintain hydration (Düsterdieck et al., 1999).  In these cases, a syringe/paste version of electrolytes may be the easiest way to ensure rapid intake of electrolytes and prevent an imbalance from escalating and creating organ system dysfunction. 

So how do you time supplementing electrolytes for competition season?  
Basic answer… Don’t ever stop supplementing.  As we’ve said, every horse needs some level of electrolytes added to their diet, with increased needs with increased sweating.  If you’re not sure the level of needs for your horse in your climate at a given level of work, contact your Science Supplements nutritionist to discuss your horse’s needs. 

However, if you haven’t been supplementing or if you know you’re increasing your horse’s work load or if the hot days of summer are fast approaching, it’s ideal to increase electrolyte intake weeks in advance of any significant changes in training or temperature so your horse is electrolyte prepared.  It’s much harder to recover from electrolyte or hydration imbalances than it is to prevent them, and the effects of electrolyte and/or hydration imbalances last longer than you may expect.  Even in horses adapted to high intensity exercise over multiple days, non-supplemented horses will experience electrolyte alterations from normal, and often stray farther from normal each day with back-to-back competition days (Assenza et al., 2014).  Further, even with a week in-between competitions, electrolyte variations created by the first competition can still be present at the start of the second competition a week later (Assenza et al., 2014).

How are electrolyte imbalances created by exercise? 
Primarily because sweat loss means electrolyte loss, and even trained horses experience significant sweat losses, the more exercise = more sweat loss = more electrolytes lost.  One study found that over a 4 day training period, horses in moderate work lost an average rate of around 6 kg (13lb) of sweat for a 500kg (1100lb) horse, while very heavy exercise resulted in an average rate loss of 7.8kg (17.2lb) of sweat for a 500kg (1100lb) horse (Hoyt et al., 1995).  But not all hope is lost, as horses maintained on a balanced electrolyte supplement for multiple weeks prior to exercise periods stay within electrolyte balance, despite these levels of sweat loss (Hoyt et al., 1995). 

Electrolytes and Hydration
The other reason electrolyte imbalances are related to exercise is that sweating also leads to water loss – though not at the same rate as electrolyte loss – which alters electrolyte and water concentrations in the horse’s body.  This is one of the reasons it’s harder to recover from electrolyte or dehydration imbalances than it is to prevent them.  Once an imbalance is created, both electrolyte and water intake has to recover, and you can’t really correct one without affecting the other. 

As one of the subsequent reasons we want to supplement electrolytes is due to their relationship with helping horses maintain hydration, let’s talk a little about why adding electrolytes is particularly helpful at increasing water intake and contrast it to human hydration balance.  For humans and horses, with exercise and subsequent sweat loss, we both lose water and electrolytes in sweat.  For humans, losing water and electrolytes are both a signal to our brain that we need to drink more water – as in losing water in sweat makes us thirsty, but losing electrolytes in sweat also makes us thirsty, so it’s a “double stimulus” to drink more water. 

For horses, the effects are not the same because their sweat composition (balance of water and electrolytes) is different, and they’re not as sensitive to the loss of water’s ability to create thirst (likely an adaptation helpful for wild horses without constant access to water).  Instead, what makes them thirsty is when they have more electrolytes versus water in their blood than normal, so essentially if we can create “salty blood” by administering electrolytes, horses will voluntarily increase their water intake at the same time we replace the lost electrolytes (Kronfeld, 2011).  And this effect is relatively rapid - for instance, administering electrolytes has been shown to increase voluntary water intake for 4 hours following electrolyte administration (Pagan et al., 2013), which is why it’s so important to provide unlimited access to clean water at all times for horses, but especially when they are provided supplemental electrolytes.  Further, electrolyte supplementation has been associated with better adaptation to hot, humid environments and reduced dehydration from exercise significantly better than providing water alone (Hyyppä et al., 1996), and simply providing water to a horse who has lost a lot of sweat actually makes their blood less salty and more dilute, exacerbating electrolyte imbalances and reducing the chances the horse will voluntarily drink on its own (Kronfeld, 2011). 

Electrolyte supplementation of at least sodium is warranted on a year round basis, regardless of competition or training season, but horses need additional levels and variety of electrolytes whenever exercise and/or sweat are increased.  Ideally, providing higher and more diverse electrolyte supplementation should begin weeks before changes in exercise or sweating to prevent imbalances.  If an imbalance is created, special attention should be given to replenishing electrolytes through palatable, easy to dose methods and providing unlimited access to water in order to reduce escalation of electrolyte and hydration imbalances. 

See the Science Supplements line of Electrolytes


Assenza A, Bergero D, Congiu F, Tosto F, Giannetto C, Piccione G. Evaluation of Serum Electrolytes and Blood Lactate Concentration During Repeated Maximal Exercise in Horse. Journal of Equine Veterinary Science. 2014;34(10):1175-1180

Düsterdieck KF, Schott II HC, Eberhart SW, Woody KA, Coenen M. Electrolyte and glycerol supplementation improve water intake by horses performing a simulated 60 km endurance ride. Equine Veterinary Journal. 1999;31(S30):418-424

Gordon ME, Jerina, ML. Water intake in horses fed supplemental salt compared to free-choice access to salt blocks. Journal of Equine Veterinary Science. 2013;33(5):348-349

Hess TM, Kronfeld DS, Williams CA, Hoffman RM, Waldron JN, Graham-Thiers PM, Greiwe-Crandell K, Lopes MA, Harris PA. Potassium supplementation affects acid-base status and plasma ion concentrations of horses during endurance exercise. American Journal of Veterinary Research. 2005;66:466-473.

Hoyt JK, Potter GD, Greene LW, Vogelsang MM, Anderson JG. Electrolyte Balance in Exercising Horses Fed a Control and a Fat-Supplemented Diet. Journal of Equine Veterinary Science. 1995;15(10):429-435.

Hyyppä S, Saastomeinen M, Pösö AR. Restoration of water and electrolyte balance in horses after repeated exercise in hot and humid conditions. Equine Veterinary Journal. 1996;28(S22):108-112.

Kronfeld DS. Body fluids and exercise: Replacement strategies. Journal of Equine Veterinary Science. 2001;21(8):368-375

Lindinger MI. Determinants of surface membrane and transverse-tubular excitability in skeletal muscle: implications for high intensity exercise. Equine Comparative Exercise Physiology. 2005;2:209-217.

McConaghy FF, Hodgson DR, Evans DL, Rose RJ. Equine sweat composition: effects of adrenaline infusion, exercise and training. Equine Veterinary Journal. 1995;27(S20):158-164.

Muñoz A, Riber C, Trigo P, Castejón-Riber C, Castejón FM. Dehydration, electrolyte imbalances and renin‐angiotensin‐aldosterone‐vasopressin axis in successful and unsuccessful endurance horses. Special Issue: Proceedings of the 8th International Conference on Equine Exercise Physiology. 2010;42(38):83-90

National Research Council. Nutrient Requirements of Horses: Sixth Revised Edition. 2007. Washington, DC: The National Academies Press

Pagan JD, Waldridge BM, Lange J. Dextrose does not affect rate of absorption or retention of electrolytes in idle Thoroughbreds. Journal of Equine Veterinary Science. 2013;33(5):349-350

Robert C, Goachet A-G, Fraipont A, Votion D-M, Van Erck E, Leclerc J-L. Hydration and electrolyte balance in horses during an endurance season. Special Issue: Proceedings of the 8th International Conference on Equine Exercise Physiology. 2010;42(38):98-104.

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