A host of essential body functions depend not only on the presence of electrolytes, but also the maintenance of precise concentrations of different levels of electrolytes on the inside versus the outside of cells, and even within different sections of a cell.
- The production and secretion of sweat, saliva, intestinal tract fluids, urine and mucus
- Heart contraction
- Intestinal movement (and other involuntary smooth muscle contractions, such as in the uterus)
- Absorption of nutrients across the intestinal wall and into the body’s cells
- Skeletal muscle contraction
- Nerve function
- Maintenance of normal acid-base balance (pH)
- Maintenance of normal hydration (the body containing roughly 70% water)
Electrolyte: Any mineral present in the body in an unbound (not attached to protein), ionized form. Usually refers to these minerals in blood but also applies to “free” ionized minerals in other body fluids and inside cells.
ION: Free mineral carrying an electrical charge (e.g. Ca++, Na+, Cl-)
CATION: Ion with a positive charge (e.g. K+, Na+, Ca++, Mg++)
ANION: Ion with a negative charge (e.g. Cl-, HCO3-, SO4–, PO4—)
Supplementing with sodium
In addition to sweat, the horse experiences a daily loss of electrolytes in respiratory tract secretions, urine and manure. These losses occur all year. Impaction colic is a common problem in winter and has as much to do with inadequate water intake as it does with the inability to hold optimal quantities of water in the body and GI tract because of inadequate sodium.
Sodium is the major electrolyte that controls hydration and causes thirst. It holds water in the blood stream and tissues. Thirst is triggered when the brain reads high levels of sodium in the blood. If sodium intake is low, sodium will move from the tissues surrounding the cells into the blood, pulling water with it. The blood volume is maintained at a normal level but at the expense of the tissues. Also, since blood sodium is normal, not elevated, it will not trigger the impulse to drink to bring the total body water content up to normal.
Of the major electrolytes (potassium, sodium and chloride), potassium levels are very generous in hays. Chloride also comes from hay, but levels may vary and the status may be low either with low chloride hays or in horses on restricted quantities of hay. Sodium is low to nonexistent in all types of hay and grain (except hays irrigated with high saline water) and is the major concern for electrolyte supplementation. Plain salt is sodium chloride. To meet basic needs and avoid problems related to dehydration, supplement the average-sized horse with one ounce (two tablespoons) of plain salt per day, even in winter.