An average 500kg horse has a daily requirement of 10 grams of sodium and 40 grams of chloride on a cool day doing no work (NRC, 2007). Bump the work level up to moderate and those requirements increase to 17.8 grams and 53.3 grams respectively and this does not account for hot weather. These two electrolytes are critical to the function of numerous cellular processes within your horse’s body and for that matter, yours as well!
Salt’s role in the horse’s body
Sodium plays a vital role in the functioning of the central nervous system and the transport of glucose across cell membranes. It is also the major electrolyte involved in determining the relative acidity of cell fluids and the levels of fluids inside and outside of cells. Chloride is also a major component of the fluid surrounding cells (extracellular fluid) involved in acid base balance and fluid regulation. Additionally chloride is an essential component of bile as well as hydrochloric acid a major secretion in the stomach necessary for digestion.
Sodium is the major positively charged ion in the fluid surrounding cells and potassium is the main positively charged ion within cells. The difference in the concentrations of potassium and sodium creates a concentration gradient across the cell membrane. When nerves are triggered, channels in the nerve cell membranes open and the sodium ions move into the cell. This changes the internal electronic charge of the cell from negative to positive. Gradually potassium channels open and the process is reversed. Tightly controlling the concentration gradient across cell membranes is vital for nerve cell function and therefore electrolyte levels are vital to nerve conduction and muscle contraction. A horse with inadequate sodium status may therefore have compromised muscular skeletal performance.
There are sensors in the brain that monitor blood sodium concentration. If circulating sodium levels become too concentrated a thirst response is triggered that motivates consumption of water. Water makes up just over 60 percent of a horse’s body weight and is vital for numerous bodily functions. Maintaining an adequate sodium level is not only important for neuromuscular function but for overall hydration status as well.
What happens if your horse is not getting enough sodium or chloride?
Where sodium goes water tends to follow. Therefore if circulating sodium levels drop, blood volume decreases which impacts blood pressure. With sodium being the major electrolyte in extracellular fluid and its important role in maintaining the circulatory system as well as the neuromuscular systems, there are a number of mechanisms for controlling sodium concentrations. For example, the circulatory system has baroreceptors that register blood pressure and in response to changes in pressure they send feedback to the nervous and endocrine (hormone) systems. In turn the kidneys can either hold on to or excrete more sodium depending on what feedback they receive. When circulating sodium levels are inadequate less sodium is excreted in urine. Instead the kidneys will excrete more potassium. Because water follows sodium, urine with lower sodium content will contain less water and be more concentrated. Ironically lower circulating sodium means less thirst stimulus so while water is conserved by reducing excretion, consumption of more water is not stimulated and as a result dehydration may occur.
Despite the horse’s ability to adapt well to reduced sodium intakes thanks to the various regulatory mechanisms, horses that are not consuming adequate sodium will have a low level dehydration which may become an issue should greater demands be placed on them. Horses consuming inadequate amounts of sodium are more likely to suffer from heat stress, and electrolyte imbalances than those consuming the correct daily intake of sodium and chloride. They may also have an increased risk of impaction colic due to reduced fluid consumption and flow through the gastrointestinal tract.
Other symptoms associated with inadequate sodium and chloride intake include:
• decreased feed intake
• weight loss
• muscle weakness
• decreased milk production
• constipation • decreased skin turgor (skin stays tented when pinched)
• licking objects
• uncoordinated muscle contractions
How do you best insure adequate daily intakes of sodium and chloride?
Sodium and chloride levels in forages vary and without a forage analysis it should not be assumed that they are adequate to meet daily requirements. While sodium and chloride are both added to commercial feeds to help meet requirements and aid in palatability the amounts may not be enough to meet daily needs especially in working horses. Therefore the best practice is to insure a supplemental source.
How much salt?
Luckily an easy source of supplemental sodium and chloride exists in salt. Regular table salt or sodium chloride is approximately 61 percent chloride and 39 percent sodium. Feeding 30 grams of salt a day will provide 11.7 grams of sodium enough to meet the maintenance needs of a 500 kg horse.
What about ad lib salt licks?
Many people rely on block salt as their horse’s supplemental source of sodium chloride. While horses do have a craving for sodium which will cause them to seek it out, few horses lick a block adequately enough to consume their daily requirement. A 500 kg horse needs to consume about a one kilo block of salt a month to be consuming its daily sodium requirement. Some horses consume more salt off a block if it is broken in to chunks or if loose salt is made available in a pan.
Horses should absolutely have free choice salt available to them but if your horse is not consuming adequate amounts of salt from a block to meet daily maintenance requirements consider adding about 15 grams per 250 kg of body weight to their ration everyday.
What type of salt?
Be sure to use sodium chloride not lite salt as the latter is potassium chloride and will not help maintain sodium levels. Some horses appear to prefer sea salt or Himalayan salt over regular table salt. There is no added nutritional benefit of these more gourmet forms of salt however if these are what are preferred by your horse they can be a good choice.
Can I feed too much salt?
As for whether you can give too much salt the National Research Council advises that as long as adequate water is available excess sodium will be excreted in urine and gives the maximum tolerable concentration in the ration of 6 percent of total feed intake. Research suggests that large intakes of salt may lead to gastric ulceration however the levels of salt administered in the study were significantly greater than would reasonably be given by most people.
Keep in mind that the purpose of giving salt is to provide adequate sodium to meet daily maintenance requirements not to replace sweat losses. Horses can lose large quantities of sodium and chloride in sweat and for these replacement purposes a good electrolyte supplement such as HYGAIN REGAIN should be used in addition to salt.
Providing your horse with adequate salt each day can go a long way in maintaining hydration which not only safe guards health but supports optimal performance as well.