Electrolytes for Horses

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Electrolytes are among the most frequently used equine supplements, but also the least well understood, especially the horse’s sources for them.

Electrolytes are minerals that are present in the blood and tissues in an ionic form, meaning they’re electrically charged. Those with a positive charge are called cations. Those with a negative charge are anions (see p 12, Table 1). The major electrolytes are sodium, potassium, chloride and bicarbonate. Minor electrolytes, meaning present in smaller amounts in ionic form, are calcium, magnesium, sulfates and phosphates.

Electrolytes are involved in every process that every cell in the body performs. We tend to only think about electrolytes in the summer, but they are needed year round. If you only supplement in the summer, where do they come from the rest of the time' From the diet.

Table 3 on p 12 lists the major electrolytes in the body, lost in sweat and present in electrolyte supplements, requirements for no formal exercise versus heavy exercise, and the amounts contained in a concentrated electrolyte supplement versus a typical amount of hay.

Electrolyte losses occur in manure and urine on a daily basis. As you can see from the chart, those needs are met easily by hay, except for sodium. The remaining sodium requirement is why all horses should have access to plain salt, which is sodium chloride.

In the electrolyte requirements Table 2 on page 12, the difference between rest and heavy work is the electrolytes lost in sweat over a one-hour period at ”average” rates of sweating. A horse getting good amounts of hay and free access to salt (salt contains just over 11 grams of sodium per ounce) can easily meet their electrolyte needs under most circumstances. Where you start to need more is:

• Horses sweating average amounts but working longer than an hour

• Horses working in high heat (sweat losses can quadruple)

• Horses that are heavy sweaters

• Horses that don’t consume free-choice salt well enough to meet their needs may benefit from an electrolyte supplement, but they only need the sodium and maybe some extra chloride so a much more economical choice would simply be to supplement salt.

Needing A Supplement

So, the electrolyte needs of most horses can be easily met from a proper diet and a salt block. However, there’s a catch. While you can make losses equal intake at the end of the day on a balance sheet, what really matters is if the horse is going to run short during a period of long or intense exercise during the day. In other words, only what the horse has eaten before exercise counts.

The horse absorbs sodium, potassium and chloride from the intestinal tract efficiently. Any excess over what the body requires at that time is rapidly excreted in the urine, so there’s essentially no excess stored. An exception to this is sodium, where there’s some reserve in bone, but researchers are not sure how easily this can be released when needed.

As a rule of thumb, you should figure that the electrolytes available to the horse to replace sweat losses during exercise are only as much as the horse has consumed in the four hours or so prior to exercise.

In the Electrolyte Losses In Sweat (Table 3, p 12) we list the fluid and electrolytes lost per hour in sweat under conditions of low and high sweating rates. Using the averages in the last column of the Table 2 (p 12), you can figure out roughly how much electrolytes your horse will have ”on board” when you start exercise. If your horse had about seven pounds of hay before exercise, that’s about one-third of the amounts listed there. That means he will have at least 31 grams of chloride and 50 of potassium to draw from. Each ounce of salt will provide 11.4 grams of sodium and 17 grams of chloride for a total of 48 grams chloride, 11.4 sodium and 50 potassium. The sodium is only enough for 1 hour of work at low sweating rates, but your levels of other electrolytes are fine.

Rule of Thumb: For low-to-moderate intensity exercise and average rates of sweating, a hay-based diet with one ounce of salt per hour of work in addition to the one ounce of salt baseline requirement will meet electrolyte needs.

If working longer than two hours, at high-work intensity (e.g. endurance racing) or in high heat with heavy sweating, you can get into larger losses. It might still be possible for your daily tally to come out OK, but when your horse’s sodium needs aren’t continuously met his desire to drink may be less so it is wise to replace sweat losses sooner rather than later. This is where electrolyte replacement products may come in because they are formulated to match the losses in sweat.

Let’s use the same horse as above, but instead of riding for one hour you take your horse on a four-hour trail ride. Your losses at a low sweating rate would be sodium 44.8, potassium 19.2 and chloride 84.8. If you fed your horse the same seven pounds of hay before leaving, he got at least 31 grams of chloride and 50 grams of potassium. Even with an ounce of salt also given, you’re still short 33.5 grams of sodium and 37.8 of chloride. You can correct this with 3 oz. of plain salt (34.2 grams sodium and 51 grams chloride), or you could use an electrolyte replacement product. However, if you take a look at the levels of electrolytes even in the good products, you’ll see you have to give a lot more than 3 oz. to meet the actual losses.

Rule of Thumb: The only time you really need an electrolyte replacement product is if the horse gets no hay before exercise or the amount of hay that was fed in the 4 to 6 hours before exercise is not enough to meet calculated potassium needs.

We’ve included in our products chart (p 11) only supplements that have good concentrations of electrolytes in them and no or low sugar. We’ve broken down the costs to show you how much each costs you to replace electrolytes lost during 1 hour of exercise at low sweating. For most horses, plain salt is the most economical, coming in at just 3?? for each hour of exercise.

Bottom Line

The recent increased understanding of chloride requirements (see July 2008) and levels in the diet has revised our thinking about electrolyte supplements to some extent. For many horses being used lightly, simply increasing the amount of plain salt in the diet is usually all you need to do to protect your horse.

With an eye toward budgets and the economy, take a good look at Uckele’s Pro-Lyte. It’s a price standout at 14?? per hour. If you’re feeding some hay before exercise, but not enough to cover losses , we think you’ll find a good match here.

For horses who need a supplement that matches sweat closely because of little or no hay, for good balance and best price it’s Farnam’s Electro Dex 19??. This product just noses out Gateway’s Su-Per Lyte.