Electrolyte Balance – vital to the proper functioning of a racehorse's system
/Words - Dr. Cath Dunnett
Electrolytes are essential components of the racehorse’s diet as they are vital to the proper functioning of the body’s basic physiological processes, such as nerve conduction, muscle contraction, fluid balance and skeletal integrity. The major electrolytes, sodium, potassium, chloride, calcium and magnesium are widely distributed within the body, but can be more concentrated in particular organs and tissues.
For example, the level of potassium is very high in red blood cells but quite low in plasma, and the level of calcium in blood is low, but comparatively very high in bone and in muscle cells. The body has in-built mechanisms that work to maintain the correct electrolyte balance within the tissues, fluids and cells. These modify the absorption of electrolytes in the gut, or their excretion by the kidneys. These mechanisms are not foolproof however, and electrolyte loss through sweat can be a major issue for Thoroughbreds. The sweat of the equine athlete, unlike its human counterpart, is hypertonic; meaning that horse sweat contains higher levels of electrolytes than the circulating blood plasma. Consequently, the horse loses comparatively large quantities of electrolytes through sweating.
Although the electrolyte composition of equine sweat varies between individuals, on average a litre would contain about 3.5g of sodium, 6g of chloride, 1.2g of potassium and 0.1g of calcium. From this we can see that the majority of the electrolyte lost is in the form of sodium and chloride or ‘salt’. The amount of sweat produced on a daily basis and therefore the quantity of electrolytes lost differs from horse to horse and depends on a number of factors. As sweating is primarily a cooling mechanism, how hard a horse is working, i.e. the duration and intensity of exercise and both the temperature and humidity of the environment are all significant. Horses can easily produce 10 litres of sweat per hour when working hard in hot humid conditions. Stressful situations can also cause greatly increased sweating.
For example, during transport horses can lose a significant amount of electrolyte through sweating and the opportunity for replenishing this loss through the diet may be less as feeding frequency is reduced. Use of electrolyte supplements either in the form of powders or pastes is advocated before, during and after travel, especially over long distances. A number of air freight transport companies advise trainers to use a powdered electrolyte supplement added to the feed on a regular basis given for the 3 days prior to travel. As this helps offset much of the loss normally incurred during transport and subsequently the horses arrive at their destination in better shape. Electrolyte supplementation is a valuable attribute in the ongoing battle to reduce in-flight dehydration.
Electrolytes lost from the body in sweat must be replenished through the diet. All feeds, including forages, have a natural electrolyte content and in concentrate feeds this is usually enhanced by the addition of ‘salt’, which is sodium chloride. Forages such as grass, hay, haylage or alfalfa (lucerne) naturally contain a large amount of potassium, as can be seen from the table 1 below. In fact, 5kg of hay for example, would provide in the region of 75g of potassium, which largely meets the potassium needs of a horse in training. It is therefore questionable whether an electrolyte supplement needs to routinely contain very much potassium unless forage intake is low. Calcium is another important electrolyte, but it is lost in sweat in only very small amounts and its availability in the diet tends to be very good.
Calcium is particularly abundant in alfalfa with each kilogram of the forage providing nearly 1.5g of calcium. A kilo of alfalfa alone would therefore go a long way towards replacing the likely calcium loss through sweating. In addition, the calcium found in alfalfa is very ‘available’ to the horse in comparison to other sources, such as limestone. Calcium gluconate is another very available source of calcium, however, it has a relatively low calcium content compared to limestone (9% vs. 38%) and so much more needs to be fed to achieve an equivalent calcium intake. Interestingly, there is great variation between individual horses in their ability to absorb calcium, however, scientific studies carried out at Edinburgh Vet School showed that this variability was considerably less when a natural calcium source in the form of alfalfa was fed.
By far the most important electrolytes to add to the feed are sodium and chloride or ‘salt’. The levels of sodium and chloride found in forage are quite low and due to manufacturing constraints only limited amounts of salt can be added to traditional racing feeds. A typical Racehorse Cube fed at a daily intake of 5kg (11lbs) would provide only about 20g of sodium and 30g of chloride. As can be seen from table 2 this is a fair way short of meeting the daily requirements for these particular electrolytes by a racehorse in hard work.
It is therefore very important that supplemental sodium and chloride is fed. Ordinary table salt is by far the simplest and most economical electrolyte supplement, but the downside is the issue of palatability as the addition of larger quantities of salt to the daily feed can cause problems with horses ‘eating up’. As an alternative salt could be added to the water, but only when a choice of water with and without salt is offered. Salt should not be added to the water if it puts a horse off from drinking, as dehydration will become a problem.
Inadequate water intake can also contribute to impaction colic. Saltlicks are another alternative, although intake can be very variable and we rely on the horse’s innate ability to realise its own salt requirements, which is questionable. So addition to the feed is by far the best route for adding salt or electrolyte supplements to the diet. Splitting the daily intake between two or three feeds can reduce problems with palatability.
Mixing salt and Lo Salt can make another simple DIY electrolyte supplement in the proportion of for example 500g to 250g respectively. Salt is sodium chloride (NaCl), whilst Lo Salt contains a mixture of sodium chloride and potassium chloride (KCl). This formulation provides 3g of sodium, 6g of chloride and 1g of potassium per 10g measure. This DIY mixture will replace these electrolytes in the approximate proportions that they are lost in sweat. What are the implications of a racehorse’s diet containing too little or too much of an electrolyte and how can we assess this? An inadequate level of certain electrolytes in the diet in some horses may simply result in reduced performance. In other individuals, it can make them more susceptible to conditions such as rhabdomyolysis (tying up), or synchronous diaphragmatic flutter (thumps), both of which are regularly seen in horses in training. Conversely, an excess electrolyte intake is efficiently dealt with by the kidneys and is ultimately removed from the body via the urine.
Therefore, the most obvious effect of an excessive electrolyte intake is increased drinking and urination. For this reason, the use of water buckets rather than automatic drinkers is preferred, as whilst the latter are far more labour efficient, the ability to assess water intake daily is lost. Excessive electrolyte intake can also be a causative factor in diarrhoea and some forms of colic. There is also some recent evidence in the scientific press that suggests that repeated electrolyte supplementation might aggravate gastric ulcers. However, these early studies used an electrolyte administration protocol typical of that seen during endurance racing, rather than simply a daily or twice daily administration, which is more commonly used in racing.
Supplements that contain forms of electrolyte that dissolve more slowly in the stomach, however, may be less aggressive to the sensitive mucosa. Unfortunately blood levels of sodium, potassium, chloride or calcium are poor indicators of whether dietary intake is sufficient or excessive unless it is very severe. This is because the body has effective systems for regulating the levels of these electrolytes in blood within very tight physiological limits. A creatinine clearance test, which measures the electrolyte content of a paired blood and urine sample is a much more useful indicator of dietary electrolyte adequacy.
There are a large number of commercial electrolyte products available, with a wide range in the breadth of ingredients that they contain. Consequently, they vary enormously in the amount of electrolyte that they deliver per recommended daily dose, as can be seen in table 3. In addition, whilst some glucose or other carbohydrate can help improve palatability, its presence should not compromise the amount of electrolyte that is contained within the supplement. In humans, it is recognised that the uptake of sodium from the gut is improved in the presence of glucose, while this effect in horses has not been firmly established. Electrolyte paste products are also often used either before and or after racing or travel.
These products are useful as they allow rapid electrolyte intake even when feed eaten may be reduced following racing. These electrolyte pastes often provide a more concentrated form of supplement and it is extremely important to ensure that the horse has access to water immediately following their use. Failure to do this may mean that the concentration of electrolytes in the gut actually draws water from the circulating blood, which can exacerbate dehydration. Another disadvantage with paste supplements is that if they are not formulated well, with an appropriate consistency, they can be difficult to dispense from a syringe and the horse may also be able to spit most of the product out after administration.
Some simple rules of thumb for choosing a good electrolyte are that salt should be one of the first ingredients listed on pack, as all ingredients are listed in descending order of inclusion. Additionally, be wary of supplements that taste sweet, as they may contain a lot of carbohydrate filler and little electrolyte. Some electrolyte supplements also contain many superfluous ingredients such as vitamins and trace minerals. The inclusion of these latter ingredients is largely unwarranted and their presence could cause issues with oversupply if the electrolyte is multi-dosed daily. Some electrolyte products specifically marketed towards racing may also contain bicarbonate.
The theory behind its inclusion is sound as ‘milk shaking’, whilst outside the rules of racing, has some scientific validity. However, the limited amount of bicarbonate contained in such electrolyte supplements is unlikely to have the positive effect on performance attributed to the former practice. Other extra ingredients such as pre-biotics may be more useful as they may improve the absorption of some electrolytes. In Summary, electrolyte supplementation in one form or another is essential within a racing diet. Ensuring that you are using a good electrolyte supplement is important and the quantities fed must be flexible and respond to changes in the level of work, degree of sweating and climate.
![Hydrotherapy for performanceGeorgina WhiteWhat is hydrotherapy?The historic use of water for therapeutic benefit in the equine industry has taken a leap in development in recent decades, from the humble use of cold hosing a swollen limb through to the development of water treadmills and water walkers for injury rehabilitation and performance development.Cold hosing and other forms of cooling localized areas of the body is more correctly termed cryotherapy—meaning, it aims to harness the benefits of reduction in temperature to treat mainly acute and edemic injuries. By reducing temperature of the local area, for example, a distal portion of a limb, several key functional changes occur. First, local blood flow is reduced. This is especially useful if an open wound is involved; the precapillary sphincters constrict and direct blood away from the area. Secondly, there is evidence that nociceptors, involved in the perception of pain and sensory receptors located at the end of peripheral nerve endings can be temporarily suppressed with local application of cryotherapy. Following a brief summary of cryotherapy, this article is going to focus on hydrotherapy as a mechanism for enhancing performance in the racehorse, focusing on the specific parameters of fitness that can be targeted and thus improved.Fundamental properties of waterThere are several fundamental principles of water that can be used as a recovery tool to facilitate optimum rehabilitation and ongoing performance improvement. When immersed in water, or made to move through water, the horse’s body, like the human, encounters a medium for which it is not designed, and locomotion is of limited efficiency. It is in fact the imposed limited efficiency that is useful in different training contexts—it forces the body to work harder than on dry ground, thus improving fitness and better preparing the horse’s body for future athletic tests. Similarly, the method of human altitude, or hypoxic training, is where the body will learn to produce the same amount of energy with a significantly lower available amount of oxygen and thus benefit at a later date in a competitive environment.First, and most important in an equine fitness protocol, is the viscosity of the water creating resistance; the resistance offered by water is greater than that experienced in locomotion on dry ground, therefore requiring greater overall effort to move through it. Exercising in water has shown to provide up to 15 times the resistance of exercising on land. This factor alone means that the trainer can achieve a far more challenging training environment without the horse experiencing the concussive forces on the limbs associated with high-end aerobic or anaerobic land based exercise, such as works on a gallops. Resistance also works indirectly at lower water levels whereby horses will choose to step over the water in a bid to avoid resistance. Therapists then utilize this to gain increased flexion at limb joints (further discussion of this throughout the article).Hydrostatic pressure is the pressure exerted on an object when immersed in water. Depth of immersion is an influential factor with greater depth correlating with greater pressure. Depending on the type of hydrotherapy system used, the benefits of hydrostatic pressure will vary. For example, greater hydrostatic pressure will be exerted when using a swimming lane with depths of up to two meters, as opposed to depths of 30-60cm of water on a treadmill. Application of hydrostatic pressure greatly benefits the recovery processes, acting in a similar way as compression bandages. The pressure reduces the formation of edema, or swelling, and improves the elimination of muscular by-products such as lactic acid and carbon dioxide.Buoyancy is not utilized in the same way as it is in humans and small animal hydrotherapy, except in the use of swimming lanes; this is partly due to the obvious size difference and limitations associated with submerging a horse almost completely in water. Buoyancy is achieved when the weight of the fluid displaced by the body is equal, also accounting for the force of gravity on the body. To remain buoyant, the two forces must counterbalance one another. Once this balance occurs, the body is essentially weightless, allowing exercise without the impact of joint load experienced in land-based exercise. These properties act together during water-based exercise to produce the increased benefits to the horse’s fitness discussed in this article.What happens during a hydrotherapy session?Horses are typically introduced to the hydrotherapy equipment to acclimate them and ensure they will be relaxed while exercising. It is important for the horse to establish a relaxed frame when working on the treadmill or in the hydrotherapy pool to prevent any stress-related or compensatory posture during the workout. As we know from land-based exercise, if a horse is stressed, they are likely to tire more quickly; so in order to utilize this workout, acclimation is beneficial.When using a treadmill, it is typical that the horse warms up on a dry treadmill prior to adding water. As with land-based exercise, a thorough warmup ensures adequate preparation of the horse’s muscles to be ready for harder work during the session.The bodily systems during exerciseDuring a hydrotherapy session, the horse’s different bodily systems will be affected in several ways. But essentially, the efficiency and smooth-running of these systems all contribute to overall performance quality, and any deficiencies will act as an overall limitation.The cardiovascular system is often considered to be the horse’s engine during locomotion, working with the respiratory system in concert to provide the horse with the oxygen needed for exercise as well as dispelling by-products. Working as a muscular pump, the heart delivers oxygen and nutrient-rich blood across the body via a network of blood vessels that develops further with long-term consistent exercise. Supplying this oxygen are the nasal structures; as obligate nasal breathers, horses must breathe through their noses. Flaring of nostrils and dilation of the horse’s larynx work to provide a greater cross-sectional area of space for oxygen uptake. When exercise begins, the previously oxygenated muscles begin to work and enter temporary oxygen debt. The cardiovascular and respiratory system combat this by working harder to produce a continual supply of oxygenated blood by increasing the number of breaths taken per minute, thus increasing oxygen intake. During hydrotherapy exercise, the respiratory system will be required to deliver elevated levels of oxygen and removal of increased quantities of carbon dioxide. This is because the horse begins to work towards the higher levels of aerobic exercise. At rest, the horse will be taking in approximately 60 liters of air per minute; when moving towards moderately strenuous exercise, this can increase to as much as 2,250 liters of air per minute.From here the heart increases in beats per minute to keep up with this demand. When still working with oxygen the exercise is considered aerobic; when the horse reaches a speed or exercise intensity where they require greater oxygen than is available, the horse will begin working anaerobically. In a hydrotherapy setting, the treadmill can be considered more the equivalent of strength and conditioning training where heart rate does not rise significantly. On the contrary, swimming increases heart rate significantly without the concussive forces of traditional gallop work. This is when the horse is unable to utilize oxidative processes quickly enough—also known as maximum oxygen consumption (VO2max). Any further energy must be generated by anaerobic glycolysis. The horse cannot sustain long periods of anaerobic exercise, but instead the horse’s aerobic capacity becomes greater and thus delays onset of the anaerobic exercise. Incidentally, horses also experience respiratory locomotor coupling in higher intensity canter and gallop work—a phenomenon that epitomizes the efficiency of the horse as a performance animal. The stride and breath are in sync at a harmonious 1:1 ratio; they must lengthen their stride to increase their speed.From a fitness point of view, the respiratory system is often considered the horse’s limiting factor where minimal conditioning takes place of the related structures. Additionally, the horse’s respiratory system is highly specialized for exercise. This means that any damage to or deficiency of the respiratory system can have significant influence on overall performance. Unlike in the human, the horse’s resting heart rate does not lower with increased fitness; therefore, opportunities to measure fitness are reduced to monitoring during exercise and in the recovery phase. Fitness testing methods may include blood-lactate tests, monitoring of respiratory and exercising heart rate, recovery rate from exercise—with the fitter the horse, the quicker the recovery rate. Like on dry treadmills, the controlled indoor nature of the hydrotherapy environment lends itself well to applying various fitness testing equipment as opposed to some of the environmental constraints often found in-field exercise environments such as out on a gallops.In contrast, to the respiratory system, the horse’s muscular system has great potential for improvement, and targeted use of hydrotherapy can be hugely beneficial. Muscles are arguably the most adaptive structures in the body; consistent and targeted exercise makes them effective energy providers and force producers. As part of muscle development, the individual muscle strands (myofibrils) increase in thickness (diameter) and muscle cell length; increase in muscle cell number is limited to the prenatal and immediate postnatal development. Therefore, muscle growth in the adolescent horse primarily concerns increased thickness of fibers. During exercise, miniscule micro-tears occur that are repaired and result in greater cross-sectional area of muscle mass over time. It is this occurrence that dictates the need for adequate rest and recovery following a period of exercise in order to allow these micro-tears to repair themselves fully.Once the horse has achieved a diet of quality protein and a positive energy balance (i.e., more energy going in than is being used), the horse can begin to build muscle. There is a direct relationship between the range of motion available at a joint and the likely surrounding muscle mass. If the horse has a greater healthy range of motion, then this promotes development of quality muscle or hypertrophy. If the opposite occurs, a horse with a restricted range of motion at a joint, either due to pathology or weakness, lesser work is done at the joint resulting in long-term atrophy of muscle. Using a treadmill in shallow water helps to facilitate this relationship by providing a stimulus to increase range of motion. The horse increases flexion at the hip and elbow joint, for example, to clear 2-3 inches of water and perhaps increases range of motion at the affected joints by 10-20 degrees; when doing this consistently during a session, the 10 degrees increase in range per stride suddenly becomes very influential on work done by muscles.Hydrotherapy as a correctional aidAs well as being used to develop muscle in the generally poorly muscled horse, hydrotherapy has been proven anecdotally to be an excellent method of correcting maladaptive or asymmetrical muscle buildup. This may have occurred following injury or from overuse of one side of the body. There are emerging clinical controlled trials looking at the benefits which are linked at the bottom of this article. Using a treadmill to work the horse in straight lines can be particularly useful where exercise on a circle is contraindicated. As mentioned above, the intricate control that the trainer has, coupled with the ability to view almost every angle of the horse during water treadmill exercise, means that the exercise can be quickly adapted to suit the horse’s capabilities. For example, if the horse is tiring significantly or beginning to compensate, the intensity can be adjusted quickly instead of the horse adopting a maladaptive gait to continue.Unless the distinct biomechanical effects are explained, one may wonder how and why in some cases the small amount of water on the treadmill is beneficial to the horse’s performance and fitness. First, we must consider the proprioceptive influence of water on the horse: Proprioception refers to the horse’s self-awareness and ability to place their limbs correctly; water provides stimulation to this additional sense. By adding just a small amount of water to the treadmill, say around coronet band height, the horse begins to increase the flexion through their limbs to “clear the water” as the air space above the water provides the path of least resistance. With increased flexion comes increased work done by the muscles, in particular the limb flexors. Working this much harder you begin to see the horse really use their body—lowering of the head, engagement of the core musculature, and hindlimbs stepping underneath their barrel. By raising the water further, you are able to increase these benefits to a point. Individual horses will differ, but they will then begin to walk “through” the water rather than stepping over it; here the trainer is then able to utilize the property of resistance further.Aside from the benefits of variation on the horse’s energetic body systems, the horse’s mental state greatly benefits from a change in surroundings. A number of studies as well as anecdotal evidence shows the benefit of variation in a training routine and avoiding mental “burnout” from repetitive training environments.Typical hydrotherapy protocolsThe use of interval training is commonly used in land-based exercise and can also be utilized in the hydrotherapy setting whereby repeated spells of hard work are interspersed with rest or less intense work, allowing the horse to recover to some degree their resting heart rate. Consistent use of this training method conditions the horse’s cardiovascular and muscular systems—over time requiring the horse to recover quicker before commencing the next spell of exercise. When using a water treadmill, spells of high-intensity exercise can either take the form of increased speed or increased water depth; and the trainer can elect to use this in varying forms to suit the trainer’s desired outcomes for the horse. Different centers will work differently, but a typical 10% water fill will reach approximately to the horse’s coronet band, eliciting a proprioceptive response and making the horse reach up and over the water. This is generally considered a height that will begin to tone muscles already present. A 30% treadmill fill will typically reach the fetlock or low cannon bone; here a similar response is seen with increased flexion through the limb joints as the horse steps higher to clear the water. With this, there is greater vertical displacement of the pelvis. Typically you will see an increased rounding of the spine and engagement of the horse’s core musculature. Next you have a 50% fill—generally water reaches the carpus height. This harnesses a different water property in that the horse now moves their limbs through the water, utilizing resistance of the water. A multifaceted, well-rounded hydrotherapy session would typically include short spells at various heights once the horse was well-established working on the treadmill.An example interval session on a water treadmill may take the form of:1-2 minutes dry treadmill warmup; speed generally measured in m/s and adjusted according to the horse’s natural walking speed.1-2 minutes at lowest water height to provide a gentle increase in stimulus and workload done by the horse’s body.Several bursts of work at various lower heights, possibly increasing and decreasing speed accordingly.At the peak or middle of the session, the highest water height for that horse may be selected for a shorter time; this may be where the horse works anaerobically for a period of time depending on fitness.Depending on fitness and desired outcomes, the horse may continue with a couple more spells of lower intensity work before performing a cool down on the dry treadmill.At this time, a trainer may choose to monitor the time taken for the horse’s vital signs to return to pre-exercise levels.A look at the different equipment on the marketMany commercial establishments now offer hydrotherapy sessions for equines with centers offering various services, including swimming pools, water walkers and treadmills. It is important for the therapist or trainer utilizing these to correctly clinically reason their use and apply correct treatment protocol in order to benefit performance and rehabilitation.If the trainer wishes to have a high degree of control over the various parameters available, then a water treadmill would be a suitable choice—with speed, water depth and incline all manageable via a set of controls. This means that bespoke interval training programs are easy to design for targeting specific aspects of each horse’s fitness. On the other hand, a swimming lane also provides a challenging workout for the horse where the trainer can still influence rest breaks between each length repetition without the need of fine tuning the controls; and horses will generally swim at their own pace.When considering if training on a circle or in straight lines is preferable, the trainer has several options. Water walkers will train the horse on a circle with the inside limb taking greater load and the outside limb is required to complete greater ground coverage. On the contrary, both swimming lanes and water treadmills will train the horse in a straight line, which is often considered beneficial in a rehabilitation setting, especially for gait correction, rehabilitation of spinal pathology and straightness training. Training on a circle does have its benefits when applied at the correct time in a rehabilitation program, but as with most training, an adopted ethos of “little and often” is practical. Using a swimming lane for horses that are weak through the back or have previous back pathology would not be ideal given the fact that horses generally swim quite hollow through their backs, keeping their noses up out of the water to breathe. This posture is counterproductive for the horse with back pathology where a rounded, engaged and lengthened spinal posture is beneficial for long-term musculoskeletal health.[insert diagram horse on inclined treadmill with hip in flexion with vertical arrow showing increased flexion required]When it comes to the utilization of buoyancy and hydrostatic pressure, the swimming lane is the most effective method, given that it provides the greatest degree of body submission under water. It will provide the greatest degree of whole-body resistance when compared to the water treadmill, where water depths may not reach above hock height.[insert two images: one of long low posture working in treadmill, one of inverted back posture, ideally skeleton]In summary, having reviewed the physiological effects of exercise in a hydrotherapy application, the use of hydrotherapy should be considered as an adjunct to a horse’s training regimen. It is not limited to use in times of injury but instead as a potentially highly influential additional training method for a trainer’s repertoire.Thanks to Dr. Jessica York for her assistance in the development of this article. Further research studies concerning hydrotherapy can be found below:Kinematics of the equine axial skeleton during aqua-treadmill exercise’ York, 2017Effect of water depth on amount of flexion and extension of joints of the distal aspects of the limbs in healthy horses walking on an underwater treadmill’ Mendez-Angulo et al., 2013Photo ideas:1) a horse on a water treadmill on an incline, ideally taking a forward step with their hindlimb to show the increased hip flexion during incline2) one image of long and low/ horse working over their back on a treadmill in a good posture3) an inverted posture/ skeleton (I will caption with info)4) horse at a stretched/ fast gallop (side view- that can possibly be annotated with the following around the image:-Arytenoir cartilages open-Trachea transports airflow-thoracic cavity loaded-forelimb reaches forward (free flight phase= inhalation)-forelimb strikes ground = exhalation5) horses on a Water Walker](https://images.squarespace-cdn.com/content/v1/517636f8e4b0cb4f8c8697ba/1603539700125-24NC0O8BZE74WRDTNOMF/DSC_7914.jpg)
