Salt – Essential for Life
Salt is an essential nutrient. It is not produced by the body, but it is required for life. Horses have an innate appetite for salt. When available, most horses will consume enough salt to meet their needs.
Salt is made up of the minerals sodium and chloride. Sodium is important for muscle contraction, conduction of nerve impulses, and digestion of protein. Sodium also plays a key role in the absorption of nutrients in the small intestine. Chloride is essential for the maintenance of blood pH and enhances the transport of carbon dioxide from tissues to the lungs.
Since pasture grasses and hays contain little sodium, salt (sodium chloride) is often added to concentrates formulated for horses. Free-choice salt, either plain or trace-mineralized, can also be offered to horses. A salt block is the most common form of sodium chloride that is fed to horses.
While salt blocks were originally designed for animals that have rough tongues, such as cattle, they are also suitable for horses. However, if a horse bites or gnaws at the corners of a block, it is possible that he is not getting enough salt by licking the block. Therefore, it might be preferable to feed loose salt in this scenario. If loose salt is provided in the pasture, it should be placed in a covered feeder. Also consider placing salt in at least two widely-spaced locations to ensure all horses have access to salt, especially if there are some that are aggressive in the bunch.
Trace-mineralized salt mixes generally contain low levels of other minerals. In most cases, horses will not get enough other minerals to meet daily requirements. Therefore, it would be wise to also feed a supplement that contains balanced levels of vitamins and minerals. In certain instances, a horse may consume too much trace-mineralized block, which might lead to overconsumption of some minerals.
Horses rarely consume too much salt. However, salt toxicosis may occur when water is limited or unavailable. Horses who eat too much salt may exhibit signs of colic, diarrhea, frequent urination, weakness, and recumbency. In advanced cases, horses may eventually die.
When horses do not have access to salt over a period of weeks to months, salt deficiency will develop. Horses with salt deficiency may exhibit pica (eating unusual things), and may lick or eat objects that have trace amounts of salt. If salt deficiency is not resolved, horses may become dehydrated, lose weight, and in severe cases, horses may completely lose their appetites.
In most cases, horses eat enough salt to meet their requirements. Salt should be offered ad libitum, especially to horses that are exercised heavily and frequently and when horses are exposed to high environmental temperatures and humidity.
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Kentucky Equine Research, 2003. The Nitty Gritty on Salt. http://www.equinews.com/article/the-nitty-gritty-on-salt