Although horses sweat during the summer and need to drink more water, we see more problems occurring in the winter with horses not drinking enough water. The weather is cold and horses don't believe they need to drink, so they have decreased water consumption and mild dehydration. Mild dehydration causes dry areas to develop in the intestine, causing decreased intestinal function, and this combination can lead to impaction colic.
To encourage a horse to drink you have to know what stimulates thirst and Dr. Clair Thunes with Summit Animal Nutrition indicates that high concentrations of sodium in the blood stimulate thirst. Sodium is just one of the three most important electrolytes in horses and the other two are potassium and chloride. An 1100-pound horse requires 10 grams of sodium, 25 grams potassium and 40 grams chloride per day. Forage is the basis of the horse's diet and forage is a really good source of potassium but not a good source of sodium. Many owners give their horse salt blocks but most horses will not ingest enough salt from a block. For a horse to get 10 grams of sodium, they need to eat about two tablespoons of table salt. You can purchase commercial electrolyte products but many of these contain a large amount of sugar and in these cases, there may not be enough chloride to satisfy the horse's requirements. In many cases, you can provide these electrolytes much less expensively and just as effectively by adding to your horse's ration two tablespoons of regular table salt and one tablespoon of lite salt twice daily.