Sweating allows the horse to regulate its body temperature. During intense exercise, such as a training or competition, horses sweat as a result of an increased body temperature. Especially when the environmental temperature increases horses will sweat more to regulate their body temperature. When horses sweat for prolonged periods, they lose fluids and electrolytes. Electrolytes have important functions in the body, such as maintaining the fluid balance. Therefore, it is important to provide enough electrolytes through their diet to prevent dehydration.
Electrolytes are electrically charged minerals that are important for hydration, nerve impulses and muscle contractions 1. The most important electrolytes in the body are Sodium, Potassium, Chloride, Magnesium and Calcium.
Sodium, Potassium and Chloride are the main electrolytes that have an effect on the distribution of water in the body 2. The correct ratio of these electrolytes in the body is essential for maintaining a favourable cellular and extracellular environment 2. Sodium and Potassium are both cations (positively charged electrolytes) and Chloride is an anion (negatively charged electrolytes) responsible for maintaining the body's acid-base balance and regulating osmosis 2,3. Sodium and Chloride are both found in extracellular fluid while Potassium is found in cells, mainly in muscle tissue 2. Potassium is also important for nerve signalling and muscle contractions.
Electrolytes help keep fluid levels in balance and thus prevent dehydration of the body 4. When the horse is at rest, the fluid and electrolyte balance is in homeostasis. When the horse starts to move actively, the horse's body generates a lot of heat increasing body temperature 5. If the environmental temperature is lower than the horse's body temperature, the horse can exchange heat with the environment by evaporating moisture on the skin, i.e. by sweating 6,7. As mentioned earlier, the horse loses fluids and electrolytes by sweating 8. The longer the body temperature is elevated the more the horse sweats and thus loses more fluids and electrolytes. If the environmental temperature is higher than the horse's body temperature, i.e. at temperatures above 36 ̊C, the horse will sweat more but will not be able to cool down as the body is not able to release the heat to the environment 7. It is therefore extra important to provide the horse with sufficient water and electrolytes during these conditions.
Through research, Zeyner et al (2014) developed a scoring system that estimates how many litres of sweat the horse loses through exercise. The scoring system uses 5 scores and the amount of sweat lost is estimated between 1 and 18 litres. This allows one to anticipate how much fluids and electrolytes the horse will require after exercise to replenish and maintain the fluid balance. However, this study was conducted with ambient temperatures, and the horses' training sessions were scored as low or medium intensity. Therefore, it is suggested that different conditions may cause the horse to sweat more or less and therefore the electrolyte and fluid requirements may vary.
As the horse sweats and fluid and electrolyte losses occur, the acid-base balance in the body decreases. To compensate for these losses, the body can ensure that electrolyte absorption from the digestive system increases 9. In addition, the kidneys ensure that if an insufficient amount of electrolytes are absorbed from the digestive system, less fluid, Sodium and Chloride are lost through urine 9.
Roughage and fibre in the horse's diet also affect the fluid balance in the horse's body. Warren et al (1999) investigated the effect of a high-fibre diet on water intake and intestinal fluid levels. This showed that a high-fibre diet causes horses to drink more regularly and absorb more fluids in general. In addition, due to the amount of roughage and fluid intake, the intestines retain more fluid which can positively affect the fluid balance when the horse starts actively moving and sweating.
As mentioned earlier, it is important to provide the horse with enough electrolytes through the diet. An electrolyte deficiency due to excessive sweating but no access to electrolytes to replenish losses can lead, for example, to dehydration, fatigue, recurrent muscle spasms, stomach ulcers, colic, neurological disorders and, in severe cases, rhabdomyolysis (excessive and accelerated breakdown of muscle tissue) 11,12. Sufficient roughage and concentrate feeds will provide the horse with the necessary electrolytes for body maintenance or after minimal fluid and electrolyte loss due to low-intensity exercise. However, this is not sufficient when the horse loses a higher amount of electrolytes through sweating. It is therefore recommended to add dietary supplements containing the necessary electrolytes to the diet. This can be achieved by feeding a supplement one hour before training, competition or transport or afterwards to replenish the losses 1. Most electrolyte supplements are mixed with drinking water to allow the horse to absorb sufficient fluids and electrolytes to hydrate or are added to the feed.
Synovium Electrolytes Q, from Synovium's supplement line, is a dietary supplement that can be added to the ration to balance the electrolyte balance after the horse has sweated.
References
1. Lindinger, M. I. (2022). Oral Electrolyte and Water Supplementation in Horses. Veterinary Sciences, 9(11): 1-13.
2. Coenen, M. (2013). Chapter 10 - Macro and trace elements in equine nutrition. In: Geor, R.J., Harris, P.A., & Coenen, M., (Eds.). Equine Applied and Clinical Nutrition. Saunders Elsevier: China.
3. Groenendyk, S., English, P. B., & Abetz, I. (1988). External balance of water and electrolytes in the horse. Equine Veterinary Journal, 20(3): 189–193.
4. Waller, A. P., Heigenhauser, G. J. F., Geor, R. J., Spriet, L. L., & Lindinger, M. I. (2009). Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses. Journal of Applied Physiology, 106: 91–100.
5. Lindinger, M. I. (2008). Sweating, dehydration and electrolyte supplementation: Challenges for the performance horse. European Equine Health and Nutrition Congress, 28-45.
6. Zeyner, A., Romanowski, K., Vernunft, A., Harris, P., & Kienzle, E. (2014). Scoring of sweat losses in exercised horses - a pilot study. Journal of Animal Physiology and Animal Nutrition, 98(2): 246–250.
7. Jenkinson, D. M., Elder, H. Y., & Bovell, D. L. (2006). Equine sweating and anhidrosis Part 1-equine sweating. Veterinary Dermatology, 17(6): 361-392.
8. Assenza, A., Bergero, D., Congiu, F., Tosto, F., Giannetto, C., & Piccione, G. (2014). Evaluation of serum electrolytes and blood lactate concentration during repeated maximal exercise in horse. Journal of Equine Veterinary Science, 34(10): 1175–1180.
9. Coenen, M. (2005). Exercise and stress: Impact on adaptive processes involving water and electrolytes. Livestock Production Science, 92(2): 131–145.
10. Warren, L. K., Lawrence, L. M., Brewster-Barnes, T., & Powell, D. M. (1999). The effect of dietary fibre on hydration status after dehydration with frusemide. Equine Veterinary Journal. Supplement, 30:508–513.
11. Fowler, M. E. (1979). Exhausted Horse Syndrome. Journal of the South African Veterinary Association, 85-86.
12.Walker, E. J., & Collins, S. A. (2017). The effect of exercise intensity and use of an electrolyte supplement on plasma electrolyte concentrations in the standardbred horse. Canadian Journal of Animal Science, 97(4): 668–672.
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