We’ve all heard of chloride. It’s the ”Cl” mineral that tags along behind sodium in sodium chloride or potassium in salt-alternative products. You probably also know that chloride is the major mineral in electrolyte supplements matched to sweat composition. It’s required to produce stomach acid (hydrochloric acid), regulate fluid balance in cells, control the excitability of muscle and nervous tissue, produce sweat and is the major negatively charged electrolyte in the blood and tissues surrounding the cells.
Despite all the body functions that require chloride, however, it’s received little attention in equine nutrition — at least until now.
We know the horse needed chloride, and know large amounts were lost in sweat, but no daily requirement had been set. In fact, the daily requirement was actually unknown. It was simply assumed that a horse that was getting enough salt (sodium chloride) to meet their sodium requirements would also automatically get enough chloride. Turns out that was way off.
Low blood chloride is the most common electrolyte abnormality found in horses that work for longer than a two-hour period. Sweat is the major avenue of chloride loss in an exercising horse.
Even at low rates of sweating, a horse will lose at least 10 grams of chloride per hour when exercising. If that horse’s diet contains a typical 1 ounce of salt, he gets only 17 grams of chloride from that source. No wonder low blood chloride is the most common electrolyte abnormality.
Because of some detailed work done in Europe on chloride requirements in horses, the 2007 National Research Council (NRC) has, for the first time ever, set a maintenance chloride requirement of 0.08 grams per kilogram of bodyweight. This means an 1100-lb. (500 kg) horse needs 40 grams per day of chloride.
As mentioned, an ounce of salt provides 17 grams of chloride. This means that even if you’re using an electrolyte supplement to carefully replace sweat losses, the horse is starting out with a deficit of 23 grams of chloride (a full article on electrolyte products is scheduled for our August issue).
How could estimates have been that far off without more horses showing serious problems'
The answer is the base diet. Versions of the NRC Nutrient Requirements For Horses prior to 2007 gave no recommendations for chloride or any references for levels present in the diet.
The new version does list chloride levels in feeds and grains. Hays contain anywhere from 0.45% to 0.9% chloride, with mature cuttings higher, while grains, meals and brans are much lower at 0.08 to 0.16%. Beet pulp is also low at 0.18% while fats and molasses contain no chloride.
It’s That Day That Counts
A horse that doesn’t start exercise with a supply of chloride from hay already in its intestinal tract can run into performance problems related to alkalosis with long-duration exercise.
For racehorses, this raises another type of problem. Sodium bicarbonate administration is sometimes used as a form of ”doping” to offset the acid produced during high-speed exercise and therefore improve performance. Many jurisdictions test for this.
A racehorse on a high-grain, low-hay diet may be flirting with low chloride levels at baseline if sweat losses aren’t being adequately replaced. If the horse is deprived of hay on race day, as they often are, hypochloremia and alkalosis could occur, resulting in a positive test for bicarbonate doping.
To meet their baseline chloride deficit a horse would have to eat about 8.5 pounds per day of a low-chloride young cutting of hay. This isn’t a problem with most equine diets, but it could be if the horse is on a complete feed that is less than 50% hay. It could also be a problem for an endurance or trail horse that is working hard all day without having consumed that critical ration of hay before starting.