Metallic element, electrolyte. The main extracellular cation (positively charged ion) found in extracellular fluid and blood plasma. Sodium is essential for transmission of nerve impulses, in maintaining acid base balance and regulating osmosis throughout the body. Sodium content of natural feeds like forages is low so sodium in the form of salt is often supplemented, especially for working horses. Absorbtion of ingested sodium can reach as high as 96% when body stores are low, and it is also conserved by the kidney when necessary.
Sodium depletion may result in a pica – an abnormal appetite, with licking of anything which may contain salt. In acute deficiency, appetite is depressed and may cease altogether, gait becomes unsteady and muscle twitching may become evident. Excess salt can also become toxic, and the maximum safe level is 6% of dietary dry matter.