Integrity Matters' vets continue their look at electrolytes, this time with a focus on chloride.
The saying is "where sodium goes, chloride follows". Read on for an overview about what this means inside the horse’s body.
What is chloride?
Chloride is an electrolyte located in all body fluids. It is essential for life. Chloride is also a major component of the fluid surrounding cells (extracellular fluid) involved in acid base balance and fluid regulation. Its levels are tightly controlled to prevent cellular dehydration or water retention from occurring.
Like other electrolytes such as sodium and potassium, high levels of chloride are lost in horse sweat. Chloride is very important to the high-performance of the racing Standardbred.
What chloride does:
Chloride levels in the body usually change in proportion to changes in sodium levels. Calcium and phosphorus absorption and retention are also influenced by chloride levels.
Chloride also plays an important role in the equine athlete by maintaining the body’s acid/base balance, transmitting nerve impulses and regulating the movement of fluid in and out of cells.
Chloride is essential for digestion. It is present in both stomach acid (also known as hydrochloric acid) and bile. Insufficient levels of hydrochloric acid in the stomach stops amino acids being digested.
Amino acids are the building blocks for all of the protein in the body including muscles, skin, hooves, the major organs and chemicals such as hormones and enzymes that are essential for normal body functions.
Where chloride comes from:
Chloride is found in forage (hay, pasture, chaff etc). Electrolytes are absorbed very efficiently across the gut wall. Much of the chloride in the intestine comes from hydrochloric acid that had been secreted in the stomach to break down the original food material.
Where sodium goes, chloride follows:
Gut absorption of sodium is an active process and gut absorption of chloride is a passive process. Chloride follows sodium due to the electrical gradient that is created by sodium absorption. In simple terms, this occurs because sodium is positively charged, and chloride is negatively charged. The negatively charged chloride passively follows chloride across the intestinal lining to neutralise the positively charged sodium.
What happens if chloride levels are too high or too low:
A range of medical conditions are associated with both high and low chloride levels in the horse.
As mentioned above, chloride levels are closely linked to sodium levels in the horse’s body. This means that the interpretation of high or low chloride levels starts by checking whether the sodium levels are proportionately high or low.
Scenario 1: chloride levels are high and sodium levels high - it could be that water deprivation (reduced water intake) or diarrhoea (increased water loss) might be to blame.
Scenario 2: chloride levels are high and sodium levels are normal - it could be that the horse is experiencing acidosis and further testing would be required to understand the underlying reasons.
Scenario 3: chloride levels are low and sodium levels are low - a possible explanation could be that horse has been sweating excessively.
Scenario 4: chloride levels are low and sodium levels are normal, it could be that water retention is occurring in the body due to an underlying condition such as heart or kidney disease.
How do you ensure your racehorse gets the right amount of chloride:
Horse diets that are not supplemented with salt may cause disturbances of fluid and mineral balances when a horse is losing electrolytes with heavy sweating.
This is particularly true of horses competing under hot and humid conditions. As total sweat fluid and electrolyte losses in hot, dry conditions may be twice the amount of these losses in cool, dry conditions, the level of chloride (and sodium) supplementation needed will vary with changes to both workload and climate.
Regular table salt or sodium chloride is approximately 61 percent chloride and 39 percent sodium.
All horses benefit from free access to a salt lick but Standardbreds in training also need 30-60g of plain salt per day (for a 500kg horse) as they cannot obtain enough sodium from licks to replace the salt lost in sweat.
Disclaimer: Harness Racing Victoria (HRV) recommends the ingredients of any mineral salt blocks offered should be checked prior to feeding of the horse and if further advice is required, please consult with your local Veterinarian. HRV also recommends that horses should not have unlimited access to mineral salt blocks if the product contains substances such as cobalt.
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