By Hannah Botha, MSc Equine Nutrition, Epol Nutrition Advisor
At this time of year, with the summer heat, it’s common to start wondering about the necessity of an electrolyte supplement. Here, Hannah Botha from Epol educates us on the role of electrolytes and exactly when we should be considering utilising them.
What are electrolytes?
Electrolytes are minerals that, when in their solid form, bond readily to form salts, but when dissolved in water, break down into their component elements called ions.
Ions have a positive (calcium, potassium, sodium, magnesium) or negative (chloride, bicarbonate, phosphate) charge. These charges allow the conduction of electricity. These electrical charges carry vital signals across cell membranes and along nerve and muscle cells enabling functions such as:
- Muscle contraction
- Blood volume control
- Thirst regulation
- Nutrient absorption
- Organ function
- Body fluid balance
So simply put, electrolytes maintain physiological balance in the horse’s body, which is crucial for life. If the body becomes depleted of electrolytes, bodily functions can be severely disrupted with potentially life-threatening consequences.
Fortunately, hay, grazing and additional feed are normally enough to meet the daily needs of the average horse. However, once a horse starts to work harder or sweat more, feed alone may no longer be enough to maintain the required levels.
Sweating
Sweat contains electrolytes, so when a horse sweats, he loses electrolytes.
Yet, sweating is entirely necessary as a means of helping the horse to stay cool. Exercise requires energy, and utilisation of energy produces heat; in fact, 70-80% of the energy consumed by a horse is lost as heat. 55-70% of the heat generated by exercise is lost through sweating and 25% by exhalation. If a horse could not remove heat through these mechanisms, overheating would occur in less than ten minutes. Sweating in average ambient temperatures allows for fast evaporation and, thus cooling; however, in hot climates and especially humid environments, the ability to remove heat is reduced, resulting in a body temperature increase which can lead to heat stress. As you can see from this, horses with anhidrosis (the inability to sweat) are in real danger of heat stress.
Horses can lose between 4 and 15 litres of sweat an hour (depending on factors such as the environmental temperature, how hard the horse is working and how fit the horse is). A 500kg horse contains around 300 litres of water (both extracellular and intercellular), and so, as an example, a loss of 10 litres per hour during exercise would be a loss of around 3% of total body water per hour.
Although research is still lacking, it’s thought that even a 1% loss of hydration can lead to a 4% fall in performance. However, for the well-adapted healthy equine athlete, 3% body mass loss does not seem to pose serious performance problems.
The reduction in performance seen with excessive sweating is not only due to the water loss but also the large quantity of electrolytes (especially sodium and chloride) lost when a horse sweats. Losing 10 litres of sweat is the equivalent to losing 110g of electrolytes (Marlin, D).
Heat stress
It’s important to remember that horses of all types and involved in all disciplines are at significant risk of heat stress as many contributing factors exist. [end box]
Although the eventer or endurance horse is being ridden for more extended periods of time, the breed types competing in jumping and dressage are often larger, heavier horses and, therefore, at greater risk of overheating, especially as a result of long periods of warm-up. It’s also important to note that horses not sufficiently fit enough to handle the demands of competition should be monitored more carefully as they are at greater risk of heat injury.
No matter the horse or discipline, it’s vital all owners, trainers and grooms understand the signs of a hot horse, such as, but not limited to;
- Excessive sweating – horse covered in sweat and/or sweat running from the body.
- Ataxia (unsteadiness resulting from a lack of muscle control), especially when stopping after exercise.
- Blowing very hard (deep and laboured breathing).
- Panting (fast and shallow breathing).
- A high rectal temperature – above 40°C (104°F).
- Prominent blood vessels.
- Horse may show little reaction to people or the environment.
- Horse may appear distressed.
The thirst response
Of the five main electrolytes (calcium, potassium, sodium, magnesium and chloride), sodium, chloride and potassium are the three most important, and sodium is often considered the principal one as it’s the main regulator of thirst. Therefore, it is commonly suggested that sodium chloride is added daily to the equine diet. Sodium chloride is more commonly known as table salt.
The thirst response in horses is a physiological prompt to drink to prevent dehydration under normal circumstances and is dependent for the most part on electrolyte balance, i.e. when the sodium level in the blood is high, the thirst response is triggered. In cases of light water loss (such as the loss of water in faeces, urine, exhalation or light sweating), water is released, but the level of electrolytes lost is minimal in comparison, leading to a higher concentration of sodium within the blood. This causes the body to seek out water to replace the loss of water, i.e. the horse becomes thirsty.
However, when the horse sweats heavily and/or for long periods of time, water and sodium are both lost in a more similar proportion, and thus the sodium concentration in the blood does not become so high. This means the thirst response is not always triggered, explaining why some performance horses will not drink even though they are dehydrated.
Top tip
Research has found that horses prefer cold water when given a choice. However, they appear to drink larger amounts when the water is cool rather than cold so consider providing cool, not cold, water after exercise, especially to horses that tend not to drink well.
Are electrolytes supplied in the feed?
Horses cannot rehydrate by drinking water alone. They need electrolytes from feed and/or additional supplements to allow the body to hold onto the water it takes in. Therefore, forage and feed are important components of electrolyte balance.
The National Research Council indicates that a 500kg horse in no work (maintenance) requires 10g sodium, 40g chloride and 14g potassium per day.
If we have a look at the common feedstuffs used, it’s clear that some supplemental electrolytes may be needed. For example, in forage, which should be the basis of every horse’s diet, levels of potassium are generally good, with some hays containing around 1.75-2.5%, which would be enough to cover the horse’s daily needs. However, sodium and chloride levels in forage can be low (0.05-0.5% and 0.5-0.75%, respectively). This means that even if a 500kg horse were to eat 2% of his body weight per day in forage, he would only get around 5g of sodium.
Therefore, even just to meet maintenance sodium and chloride requirements, horses must have access to a source of supplemental salt.
When horses are in work, their needs increase. For example, a 500kg horse in medium-level work requires 17.8g of sodium and 53.3g of chloride 53.3g per day. Environmental temperatures and individual variances in digestion and digestibility of feedstuffs all affect the exact amount needed. Quality concentrate feeds will contain additional sodium and chloride, so first check levels in your daily feed and then add the extra to reach the desired levels, dependent on your horse’s workload.
Regular table salt is approximately 61% chloride and 39% sodium and so 30g (approx. two tablespoons) of table salt per day would be enough to provide 11.7g of sodium which would cover maintenance needs. Harder working horses would require more.
While salt can be provided via a salt block, not all horses will utilise them enough to cover their needs. They are also hard to monitor, so for performance horses especially, it’s advisable to add a measured amount.
Electrolyte supplementation
The key to a good electrolyte supplementation program is to first provide a balanced diet with the correct amounts of forage and/or concentrates and enough salt to meet the horse’s base sodium and chloride needs. Once this is in place, a product whose electrolyte composition mimics that of sweat can be selected should the horse need one (i.e. be working hard and/or sweating for prolonged periods).
Look for a supplement containing sodium: potassium: chloride in a ratio of 2:1:3.8. Some supplements will also contain magnesium, calcium and other trace elements, but these are generally considered of less importance. Be careful when selecting supplements, as some contain sugars to increase palatability. However, this often means that the electrolyte levels are lower than ideal, so choose carefully.
When using an electrolyte supplement for a working horse, it’s advisable to provide it at the same level each day; trying to guess what your horse is losing is pretty tricky and titrating your electrolytes based on the level of work you do each day is not worthwhile. Rather keep levels adequate and consistent. Also, avoid increasing electrolytes to ‘load’ before a competition. If your horse has been on regular supplementation, increasing suddenly will likely put the horse off his food/water at a time when he most needs it. It can also cause digestive disturbances such as loose droppings and/or increase the amount of electrolytes excreted because if the horse isn’t using the additional extras, his body won’t use them. Rather, wait until the workload and rate of sweating increases to provide the extra, such as during the competition itself.
The same applies for horses not on electrolytes; adding them before competition won’t fix months of under supply and so rather, assess your horse’s diet well in advance of major competitions to ensure that you are providing what is needed daily. A horse starting competition on depleted levels is more at risk of issues.
The best way to provide electrolytes is in the feed or, in the case of replacement, such as for competitions, you can use a paste. Electrolytes can be given in water, but the volume the horse will readily consume will not allow a large electrolyte intake. This means that water is not suitable for replacing electrolytes, only helping to rehydrate the horse. It is worth noting that full replacement of electrolytes after competition can take several days.
By way of example, a horse running a 120km endurance race could lose 500g of electrolytes throughout the race. Replacing electrolytes at a rate of 100g per day (on top of their regular maintenance electrolytes) would mean that full replacement would take five days.
There is such a thing as too much
Be careful when providing electrolytes to horses that may be dehydrated. The idea is that electrolyte supplementation will stimulate thirst and encourage them to drink; however, there are horses who continue to refuse to drink despite supplementation and may end up further dehydrated.
When in the intestine, electrolytes draw water from the blood into the gut. This removes water from the blood, causing the concentration of electrolytes (particularly sodium) to increase, and this, as we have said previously, switches on the thirst mechanism. If water is unavailable, the horse doesn’t drink, or blood flow to the intestines is reduced due to exercise, giving concentrated electrolytes may worsen the dehydration by causing more water to leave the bloodstream and enter the GI tract, which is not the area of most need.
In line with this, research suggests that electrolytes should be given approximately four hours before exercise. This allows horses the opportunity to drink before they begin sweating. Depending on the sport, it may also be necessary to give electrolytes and fluids during and after the competition to help them recover more quickly, but make sure that they drink, not just consume electrolytes.
Note
Research has shown that larger amounts of administered electrolytes may result in the worsening of gastric ulcers. This should be kept in mind when deciding to use an electrolyte supplement; however, generally, the recommended daily dosages of electrolytes in supplements are much lower than those seen to cause ulcers in the study.
Conclusion
As with anything, balance is key. For the average horse in little to no work, a well-balanced diet containing adequate forage and additional salt is all that’s needed. However, once the horse starts working, especially in hot conditions, a balanced diet consisting of forage, concentrates, adequate salt and additional electrolyte supplements is required.